PL151397B1 - Method for extraction of acrylonitrile - Google Patents

Description

RZECZPOSPOLITA PATENT DESCRIPTION 151 397

POLAND

Additional patent to patent no. - Pending: 87 09 17 (P. 267830)

Int. Cl. ⁵ C07C 255/08 C07C 253/34

Priority - OFFICE

PATENT

RP

Application announced: 89 03 20

Patent description published: 1991 01 31

IF and LINE

Pcrenp-w ^ go drive

Creators of the invention: Andrzej Bachowski, Władysław Ptak, Bronisław Musiał, Józef Wikierak, Jerzy Laska, Jan Strączyński,

Krystyna Kruszewska, Wiesław Noga, Andrzej Katryński, Tadeusz Gryl

The holder of the patent: Zakłady Azotowe im. Feliks Dzerzhinsky,

Tarnow (Poland)

The method of isolating acrylonitrile

The subject of the invention is a method of separating acrylonitrile from a solution obtained by absorption of acrylonitrile with water from the reaction gas of its synthesis from acetylene and hydrogen dioxide.

The method known, for example from Polish patent description No. 98 576, consists in stripping off acrylonitrile from the obtained aqueous solution with steam and, after condensing the vapors, separating crude acrylonitrile from the condensate, which is then distilled. The post-reaction gas, after absorbing acrylonitrile therefrom, is returned as so-called recycle acetylene to the synthesis reactor, introducing fresh acetylene and hydrogen cyanide into its stream. The drained liquid remaining after stripping the acrylonitrile from the solution is a waste water. According to this method, a portion of the recycle acetylene is directed along with the water vapor after the acrylonitrile absorption operation from the reaction gas and the residual gas remaining after the acrylonitrile vapor condensation operation is recycled. However, a problem not entirely solved in the prior art remains the relatively high steam consumption for stripping and the high organic content of the waste water.

According to the invention, the method of separating acrylonitrile from the solution obtained by absorbing acrylonitrile with water from the post-reaction gas of its synthesis from acetylene and hydrogen cyanide, by stripping with steam, condensation of vapors and separation of crude acrylonitrile from the condensate, consists in the fact that the steam directed to stripping, or part of it, the exhaust liquid remaining after stripping off the acrylonitrile is depressurized by means of a jet pump and sucked in the vapors of this liquid.

The exhausted liquid remaining after the stripping of the acrylonitrile in the stripper is therefore, according to the invention, additionally subjected to the reduced pressure generated over the liquid by means of a water vapor directed to stripping the acrylonitrile used as a working medium, the suction part of which is connected to the space above the exhaust liquid. .

151 397

The pressure in this space is about 0.07 MPa. All or only part of the steam introduced into the stripper can be directed through the ejector. Due to the expansion of the exhausted liquid, which is essentially a sewage, additional stripping of the remaining organic compounds, including acrylonitrile, takes place. This means, in addition to increasing the acrylonitrile yield, also reducing the organic matter content in the wastewater. Due to the expansion of the exhausted liquid, its temperature is also reduced from about 100 ° C to about 90 ° C, which means a reduction in heat loss.

The method according to the invention is explained in more detail in the working examples, the first of which is a comparative example.

Example I. To the top of the stripper column fed 20m ³ / h of an aqueous solution of acrylonitrile at a temperature of 88 ° C containing 27 g / dm ³ of acrylonitrile and 10 g / dm ³ of other compounds derived from hydrogen cyanide and acetylene. 1600 kg / h of steam at a pressure of 0.6 MPa were introduced into the tube of this column. In the stripper receives a stream of acrylonitrile, the crude containing 498 kg / h of acrylonitrile and 74 kg / h of other compounds, hydrogen cyanide and acetylene and the stream of the sump at a temperature of 103 ° C in an amount of 21 m ³ / h and containing 2 g / dm ³ of acrylonitrile and 6 g / dm ^{3 of} other compounds, constituting the sewage. The content of organic compounds in this sewage, determined as COD, was 10,000 mg 02 / dm ³ .

Example II. At the top of the stripping column, an aqueous solution of acrylonitrile was introduced in the amount, with the temperature and composition as in Example 1. 1100 kg / h of steam at a pressure of 0.6 MPa, which was the working medium of the ejector and produced a pressure of 0, were directed to the top of the column. 07 MPa in the space over the exhaust liquid remaining after stripping off acrylonitrile. In the stripper receives a stream containing crude acrylonitrile, 501 kg / hr of acrylonitrile and 81 kg / h of other compounds of hydrogen cyanide and acetylene derivatives, and the stream of the sump at a temperature of 87 ° C, in an amount of 20.5 ^m3 / h and the content of 1.9 g / dm ^{3 of} acrylonitrile and 5.8 g / dm ³ of hydrogen cyanide and acetylene derivatives, constituting the sewage. The content of organic compounds in this sewage, determined as COD, was 8,900 mg O ₂ / dm ³ .

Claims (1)

Patent claim The method of separating acrylonitrile from the solution obtained by absorbing acrylonitrile with water from the reaction gas of its synthesis from acetylene and hydrogen cyanide, by stripping with steam, condensation of vapors and separation of crude acrylonitrile from the condensate, characterized in that by means of the water vapor directed to stripping, or a part thereof, the exhaust liquid remaining after stripping off the acrylonitrile is depressurized with the aid of the ejector and the vapor of this liquid is sucked in. Department of Publishing of the UP RP. Circulation 100 copies Price: PLN 3,000