JPS5928543B2 - Method for producing α-aminonitrile - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention produces α-
The present invention relates to a method for producing aminonitrile, and is characterized in that the reaction is carried out using a reaction apparatus that is a combination of a complete mixing tank reactor and a pipe reactor.

A method for producing α-aminonitrile by reacting cyanohydrin and ammonia is known, and in this case, a large excess of ammonia is generally used to suppress the formation of by-products, but unreacted ammonia is recovered after the one-way reaction. When reuse is considered, measures are needed to reduce the excess rate as much as possible, suppress by-products, and improve yield.

There are many other problems that need to be solved in order to produce α-aminonitrile industrially advantageously. The structure and effects of the present invention will be explained while pointing out manufacturing problems. However, it goes without saying that the present invention is not limited to glycinonitrile, but can also be applied to the production of other α-aminonitriles including α-aminoprobionitrile. Glycolonitrile, the raw material cyanohydrin, can be easily obtained by reacting formaldehyde with hydrocyanic acid, but in this case, formaldehyde is generally obtained and used as an aqueous solution of formalin, so glycolonitrile is obtained as an aqueous solution of several tens of percent. can get.

There are several ways to react this with ammonia. First, when using ammonia water, a large excess of ammonia is used, so the concentration of glycinonitrile in the reaction solution is diluted, and it is necessary to remove ammonia and water from the solution after the reaction to obtain glycinonitrile. , requires a lot of effort.

Glycinonitrile has a strong affinity for water and is difficult to extract using conventional methods. If an attempt is made to separate it by distillation, since it has a high boiling point, it will be distilled out after removing ammonia and water, so it will be necessary to evaporate a large amount of ammonia and water, and the amount of heat required will be enormous. In addition, it is unstable under heat and easily undergoes coloration or deterioration when exposed to high temperatures, so the distillation operation requires some ingenuity and is quite difficult to implement industrially. In addition, when using it as liquid ammonia, for example, by adding glycolonitrile to liquid ammonia,
It is known that glycinonitrile can be obtained relatively easily and in high yield by flashing and recovering ammonia after reacting in a closed container and distilling the residual liquid.

(J. Anl. ChOm. SOc, Vol. 56, p. 2197 (
(1934)) However, when considered as an industrial manufacturing method,
The recovered ammonia must be liquefied and used again, and the ammonia recovery system such as liquefaction equipment becomes very large and the equipment cost becomes too high, making it difficult to implement. Also, the pressure in the reactor increases, so
It must be considered that container design is difficult and includes various safety issues. The present inventors considered using gaseous ammonia as an alternative to these,
This is an industrially feasible method discovered.

This is an important point on which the present invention is based. That is, after a reaction is carried out in a system in which gaseous ammonia is dissolved to a saturation concentration in an aqueous glycolonitrile solution, unreacted ammonia is flashed and recovered, and this is recycled back to the reactor using a compressor. be. According to this method, (1) ammonia can be recovered and reused very easily; That is, ammonia can be easily recovered by adjusting the temperature and pressure for flashing, and a recirculation compressor is sufficient as the main equipment for ammonia recovery and reuse. (2) Reaction conditions are relatively mild. In other words, by increasing the concentration ratio of ammonia and glycolonitrile in the reaction solution, side reactions can be easily suppressed and the reaction rate can therefore be increased, but the pressurization required by ammonia for this purpose is several times at most. It is approximately K9/Cd, and has many excellent industrial advantages such as not requiring a special pressure-resistant container. Next, regarding the problem of unreacted glycolonitrile, glycolonitrile requires care in handling due to its toxicity, and it also has the property of easily dissociating and returning to hydrocyanic acid and formaldehyde, as well as glycolonitrile. It is difficult to separate because its boiling point is close to that of nitrile.

Therefore, it is desirable that this reaction be completed in one pass and be carried out so as to leave virtually no unreacted glycolonitrile. However, as a result of kinetic studies of this reaction, it was found that in order to react substantially 100% of the raw material glycolonitrile, it was necessary to carry out the reaction for an extremely long time, which was even more inconvenient. In this case, the glycinonitrile produced is also a very unstable compound and is easily colored or deteriorated when heated. Therefore, the reaction time should be kept as short as possible, and the product should be separated from the reaction system as quickly as possible. However, it is necessary to stabilize it or use it as a raw material for other reactions. As a means of resolving these seemingly contradictory requirements, the present inventors conducted various studies and found that glycolonitrile and ammonia were reacted in a tank reactor with stirring, and the resulting reaction liquid was reacted in a pipe reactor. We have developed a method of passing the aqueous solution of glycolonitrile through a reactor using gaseous ammonia in the first stage of the reaction using a fully mixed stirred tank reactor in which a pressure of up to several kg/Cd is applied. The reaction solution after the reaction is further passed through a pipe reactor as a second stage to complete the reaction, and then flashed at normal pressure and then under reduced pressure to recover ammonia. Ammonia is recycled to the reaction system,
On the other hand, a method has been established for obtaining a reaction solution after ammonia flushing as a concentrated aqueous solution of glycinonitrile that does not substantially contain glycolonitrile. Generally speaking, it is well known to connect several reactors in series in multiple stages or to use a pipe-type reactor in order to substantially complete a certain type of reaction in one reaction. However, using several reactors in series is economically problematic due to high equipment costs and requires careful adjustment of reaction conditions, and pipe-type reactors have difficulties in supplying raw materials. .

One of the important requirements of the present invention is that after most of the reactions are carried out in a stirred tank reactor, the residual concentration of glycolonitrile is low in the reaction solution, so ammonia does not have to be newly supplied. In this case, the ammonia/glycolonitrile concentration ratio in the reaction solution does not substantially decrease, and therefore the reaction proceeds selectively. In order to explain the content of the present invention in more detail, a typical embodiment is illustrated (see FIG. 1).

V-1 is a completely mixed tank type reactor, with an aqueous solution of glycolonitrile coming from line 1 and ammonia gas coming from line 2.
Continuously supplied from The inside of V-1 is stirred by a stirrer M if necessary. There is an external heat exchanger E-1 to remove the heat of reaction, and the reaction liquid is transferred to E by pump P-1.
-1, but at the same time the control valve CV-1.
1, the liquid is drawn out continuously so as to keep the liquid level of V-1 constant. -2 is a pipe reactor with an appropriately chosen residence time in V-2. It is desirable to keep V2 warm. The reaction pressure is adjusted to maintain the pressure of V1 at a constant value. (For example, by adjusting the flow rate of newly supplied ammonia (line 8))
. The inside of V-2 is a liquid seal with almost the same pressure as the inside of V-1. The reaction liquid is returned to normal pressure by CV-1, and the flashed ammonia gas and the reaction liquid are separated by V-3. The reaction solution is withdrawn from line 5. Ammonia gas passes through the buffer tank V-4 via line 6.
The ammonia compressor C-1 boosts the pressure, and the line 7
After joining with the freshly supplied ammonia, it is recycled via line 2 to V-1. In addition, line 5
Ammonia in the reaction solution can also be further recovered by flashing under reduced pressure.

Examples will be described below, but it goes without saying that the present invention is not limited thereto. Example 1 Glycolonitrile aqueous solution was continuously supplied from line 1,
The pressure inside V-1 was maintained at 3k9/CrAG with ammonia gas, and the reaction was carried out at 40° C. for an average residence time of 30 minutes.

The inside of V-2 is a liquid seal, and the average residence time is also 3.
It is 0 minutes.

V-2 is kept warm and the temperature is approximately 40'C.

The material balance of the main lines is shown in Table 1. That is,
The reaction rate in V-1 is 89%, and if you try to increase the reaction rate with only one stirred tank reactor, the retention rate will be about 5 to 6 times as much at 98% and more than 10 times as much at 99%. It takes time,
This cannot be carried out because the produced glycinonitrile will be degraded.

Similarly, considering multistage reactors, it can be easily calculated that four reactors of the same volume are required to achieve a reaction rate of 99%. It has been calculated that the reaction rate can easily reach 99% or more if one pipe type reactor has the same volume, and in fact, the amount of unreacted glycolonitrile is practically negligible.

The yield of glycinonitrile was 93%.

Example 2 Same reactor, ammonia pressure 0.5k
When the same procedure as in Example 1 was performed except that the reaction mixture was changed to 9/CdG, the yield of glycinonitrile decreased to 90% and the reaction solution was colored black.

[Brief explanation of the drawing]

The drawings are schematic diagrams illustrating typical embodiments of the invention.

Claims (1)

[Claims] 1. In a method for producing α-aminonitrile by reacting cyanohydrin with an excess amount of ammonia relative to cyanohydrin supplied in gaseous form in an aqueous solution, the reaction is carried out in a tank reactor under stirring. and passing the resulting reaction solution through a pipe reactor to substantially complete the reaction.