JPS60345B2 - Method for recovering active ingredients from methionine synthesis exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses hydrocyanic acid-containing gas generated from a hydantoin synthesis reactor in a methionine synthesis method that includes a hydantoin reaction as a raw material for hydantoin synthesis, such as an aqueous solution of a compound consisting essentially of ammonia and carbon dioxide gas or methionine. The objective is to effectively recover hydrocyanic acid by washing with a reaction solution containing hydantoin (hereinafter abbreviated as MH) and returning the washing solution to the MH synthesis reactor system.

As a method for synthesizing MH, methyl mercaptopropionaldehyde (hereinafter abbreviated as MA) obtained by reacting methyl mercaptan (hereinafter abbreviated as MM) and acrolein in the presence of an appropriate catalyst, hydrocyanic acid and ammonium carbonate or A method of synthesis using a compound consisting essentially of ammonia and carbon dioxide gas such as ammonium bicarbonate as a raw material, and a method suitable for synthesizing a compound consisting essentially of ammonia and carbon dioxide gas such as MM, acrolein, hydrocyanic acid, and ammonium carbonate or ammonium bicarbonate as a raw material. However, in either reaction, hydrocyanic acid is usually added in excess of the number of moles of MA, acrolein, or MM added to complete the reaction. . A portion of this excess hydrocyanic acid is dissolved in the MH solution, but most of it is liberated as hydrocyanic acid gas. Methods for treating this cyanide gas include an oxidative decomposition method using an oxidizing agent such as chlorine or hypochlorite, and a catalytic hydrolysis method using an alkali metal hydroxide supported on a carrier such as alumina or silica. ) have already been proposed, but if the gas generated from the MH synthesis reactor is treated directly, either method requires a large amount of oxidizing agent or catalyst, and because hydrocyanic acid is expensive, it is not suitable for industrial use. It cannot be said that it is a medicinal process.

Therefore, as a result of various studies, the present inventors found that M
The present invention was accomplished based on the finding that an aqueous solution of a compound consisting essentially of ammonia and carbon dioxide gas, which is a raw material for H synthesis, and a reaction solution containing MH selectively and stably absorb hydrocyanic acid.

According to the method of the present invention, the absorbed hydrocyanic acid is recovered within the system, so the amount of hydrocyanic acid used is reduced, and the processing agent used to make it harmless is significantly reduced, making it different from the conventional method. It is industrially very advantageous.

Examples of aspects of the present invention will be explained with reference to the drawings.

First, hydrocyanic acid is added to the MH synthesis reactor 1 through the pipe 2, an ammonium bicarbonate aqueous solution is added through the pipe 5, and MA or acrolein, MM, and a catalyst are added through the pipe 3.

This reaction is usually carried out at a temperature of 30 to 100 degrees and a pressure of less than 9'. The gas generated from this reactor 1 mainly consists of carbon dioxide gas, hydrocyanic acid, and MM, and is sent to the absorption tower 7 through the pipe 9, where it comes into contact with the aqueous ammonium bicarbonate solution or the MH-containing reaction solution, and most of the gas is Hydrocyanic acid is absorbed and removed.

The aqueous ammonium bicarbonate solution is supplied to the absorption tower through piping 6, and the MH-containing reaction liquid is supplied through piping 11. In either case, the absorption liquid returns to the reactor 1 through the pipe 12. As shown in the drawing, a portion of the ammonium bicarbonate aqueous solution used for the MH synthesis raw material may be used as an absorbent, or the entire amount may be used as an absorbent.

Next, the present invention will be described with reference to examples, but the present invention is not limited thereto.

Example 1 1.2 moles of hydrocyanic acid and an aqueous ammonium bicarbonate solution (33 moles of N-hydrocarbonate) were continuously added to mol of MAI, and the exhaust gas obtained by performing MH synthesis was
Volume %, methyl mercaptan2. The composition was 93.4% by volume of string volume and 93.4% by volume of carbon dioxide.

The gas obtained by contacting this exhaust gas 30N〆'Hr continuously in an absorption tower under the conditions of 3000N, atmospheric pressure, and liquid-gas ratio (1 box weight % ammonium bicarbonate aqueous solution / exhaust gas star) in an absorption tower is Hydrocyanic acid 10 pm, methyl mercaptan 2. It contained % contact capacity and 20 pm of ammonia.

An aqueous ammonium bicarbonate solution that has absorbed hydrocyanic acid from the exhaust gas in the absorption tower as described above, an amount of hydrocyanic acid reduced by the amount of hydrocyanic acid absorbed, and an amount of the aqueous ammonium bicarbonate solution used for absorption, an aqueous ammonium bicarbonate solution, and MA. MH synthesis was performed again using The yield of methionine obtained by hydrolyzing the above synthetic liquid and the synthetic liquid using the absorption liquid with sodium chloride and neutralizing with sulfuric acid was 90% for both. Example 2 The same exhaust gas as in Example 1 was brought into countercurrent contact with a reaction solution containing % by weight of MHI under conditions of 40 oo, atmospheric pressure, and liquid-gas ratio of 10.

The obtained gas contained 200 ppm of hydrocyanic acid and 2.0 ppm of methyl mercaptan. Muscle volume %, ammonia 10 cape pm included.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention, in which 1 is an MH synthesis reactor, 7 is an absorption tower, 2 to 6 and 8
-11 indicate piping. Next figure 1

Claims (1)

[Claims] 1. In a methionine synthesis method that includes a hydantoin reaction, the hydrocyanic acid-containing gas generated from the hydantoin synthesis reactor is washed with an aqueous solution of a compound consisting essentially of ammonia and carbon dioxide gas, which is a raw material for hydantoin synthesis, or with a hydantoin-containing reaction solution of methionine. . A method for recovering active ingredients from methionine synthesis exhaust gas, characterized in that the cleaning liquid is returned into the hydantoin synthesis reactor system.