DE2006979A1 - Process for the production of methionine - Google Patents

Description

Registration number 2153

ρ ,, ρ, angry ™ -ftfi / $

8 million

STAMIGAftBON NV ,, HEERIiEN (the Netherlands) Process for the production of methionine

The invention relates to a process for the preparation of methionine by converting β -methyl mercaptopropionaldehyde with the aid of hydrogen cyanide and ammonia or of ammonium cyanide in methionine nitrile (γ-methyl mercapto-a-aminobutyronitrile) using a liquid reactant consisting of ammonia and water and by means of hydrolysis of the methionine nitrile obtained in an acidic medium. The invention relates in particular to reducing the amount of ammonium salt formed during hydrolysis.

As is known methionine can be produced in very high yield when the formation of the Methioninnitrils under superatmospheric pressure at a temperature between 0 and 60 ⁰ C is performed and a high weight ratio ammonia: water is maintained in the liquid reaction medium. After the methionine nitrile has formed under superatmospheric pressure, the reaction mixture is let down to atmospheric pressure and the methionine nitrile is then hydrolyzed to methionine in an acidic medium. As a result of the fact that a fairly large amount of ammonia remains in solution in the reaction mixture after the expansion, a large amount of acid, e.g. sulfuric acid, is necessary for hydrolysis in an acidic medium, which means that, in addition to methionine, a large amount of ammonium salt, e.g. ammonium sulfate, is required hydrolysis with sulfuric acid, occurs as a by-product. .

To limit the production of ammonium salt during methionine production has already been proposed to use a methionine nitrile-containing reaction

i ^ ■ ORIGINAL JN6P £ CT £ D

mixed by cooling into one rich in methionine nitrile and one rich in water Liquid layer to separate and this water layer, which at the same time still Contains ammonia and methionine nitrile, in the reaction mixture in which the Methionine nitrile is formed, so that during acid hydrolysis the methionine nitrile-rich liquid layer produces less ammonium salt.

If, in order to achieve high yields, the formation of methionine-

ο nitriles at a temperature between 0 and 60 C, at ttberatmosphärir.ehem Pressure and with a high weight ratio ammonia: water carried out in the reactant, so it is obvious that one is involved in the acid hydrolysis also tries to limit the formation of ammonium salt by the methionine nitrile-containing reaction mixture in two layers of liquid decomposed and circulate the ammonia-containing water layer, in principle can this separation can be carried out in two ways. One can use the "ethionine-nitrile-containing For the purpose of this two-phase separation, cool the reaction mixture under superatmospheric pressure or after the mixture has expanded.

In the practical implementation of this has two options it turns out, however, that such a two-phase separation is not always possible is, and especially not if you have this decomposition; under the ubiquitous Tries to apply pressure, if in a certain case one Separation in two layers can be brought about, so a strong temperature lowering of the reaction mixture is usually necessary. Furthermore has It turned out that in the case of a breakdown of the mixture into two liquid layers, the methionine-rich layer is still quite contains a lot of ammonia.

A method has now been found to match the formation of methionine nitrile under superatmospheric pressure at a temperature between 0 and 60 C and with a high weight ratio ammonia: water can be carried out in the reactant and a two-phase separation of the liquid mass can always be brought about in an economical manner; it comes In addition, the methionine nitrile-containing liquid layer only contains a small amount of ammonia.

The method according to the invention is characterized in that the methionine nitrile-containing reaction mixture is heated in a closed system to a maximum temperature of 100 ° C., the reaction mixture then with the removal of the gaseous ammonia released in the process expands, the so relaxed reaction mixture transfers for cooling into a

OfMOINAL INSPECTED

ammonia-containing water-rich liquid layer and a methionnitrile-rich The liquid layer separates, the water-rich layer is fed back into the process and the methionine-nitrile-rich liquid layer is an acidic one Subjecting to hydrolysis.

The method according to the invention is based on the finding that for a suitable separation of the reaction mixture into two liquids. speed phases, the ammonia content of the reaction mixture should not be too high and this ammonia content can be effectively reduced, by bringing the reaction mixture to one temperature in a closed system of a maximum of 100 C and then relaxed. Even though Methionine nitride is a fairly unstable compound, as occurs itself shows up to a maximum when the temperature of the reaction mixture increases 100 C no noticeable decomposition if this temperature increase in a closed system.

Wed +. The process according to the invention has the great advantage that methionine can be obtained in a very high yield and ammonium salt is obtained as a by-product in the smallest possible amount. It is also shown that when the method according to the invention is used, the ammonia-containing water layer to be returned contains only a little methionine nitrile, so that a circulating amount with a low methionine nitrile content is sufficient to limit the ammonium salt production.

To carry out the process according to the invention, the reaction mixture can after formation of the methionine nitrile under an atmosphere Pressure and with deduction of gaseous ammonia expanded, then im closed system heated to a maximum temperature of 100 C and expanded again with the deduction of gaseous ammonia, after which the Separation takes place in two liquid layers. Preferably omitted the first-mentioned relaxation of the reaction mixture and finds the temperature increase in the closed system in the presence of the educated Reaction mixture · dissolved ammonia instead.

The gaseous ammonia obtained in the process according to the invention can be used in the process, e.g. for neutralization of the acidic hydrolysis mixture. Preferably, however, the gaseous Ammonia dissolved under pressure in the surrounding water-rich layer.

The conditions under which the methionine nitrile is formed can be varied. An economically optimal result is obtained

009837/2219

if during the formation of the methionine nitrile the temperature is between 25 and Maintained 45 C, a weight ratio ammonia: water in the reactant between 1.3: 1 and 2: 1 applied and the reaction gas in the closed System is heated to a temperature between 65 and 75 C.

The heating of the reaction mixture in a closed system can be implemented in different ways in practice. Preferably the reaction mixture is passed through one or more heated tubes, which are separated from the expansion space by means of an expansion valve.

The method according to the invention is illustrated in the accompanying figure ■ explained in more detail with a schematic exemplary embodiment.

In a reactor (1) and a reactor connected in series with it (2) Methionine nitrile is formed at a temperature of about 40 C and a pressure of 6 at absolute. The two reactors are with equipped with a stirrer and a cooling jacket, via a line (3) / J-methylmercaptopropionaldehyde, via line (4) ammonia and via the Line (5) introduced hydrogen cyanide into the reactor (1).

The reaction mixture runs via line (7) into the reactor (2) and from there via the line (8) into a closed buffer vessel (9). After exiting this vessel, the reaction liquid is with the help of a Piatpe (10) passed through a tube heater (11) in which the reaction flow

o ο

The liquid is heated to a temperature of around 70 ° C using water at around 80 ° C will. The 80 ° C hot water flows to this heater (11) through line (12). The heating water goes through the pipe after use (13). After the reaction liquid in the heater (11) has the required Has reached temperature, the pressure has risen to about 10 at absolute. The reaction liquid is then pumped out with the aid of an expansion valve (14) absolutely relaxed to a pressure of about 1.2 at. Thereby the temperature goes back to about 25 C. The gaseous one that is released during this expansion Ammonia is separated from the liquid in a separator (15) and flows off via the line (16). The liquid is fed through the line (17) discharged from the separator (15) and, after cooling, goes down to about 15 ° C in a cooling system (18) through the line (19) to a separator (20). In the latter separator, the liquid separates into two layers. The liquid layer rich in ethionine nitrile passes through the line (21) into a - not shown - plant where the acid hydrolysis takes place. The water-rich liquid layer is pumped via line (22) (23) and line (24) introduced into the absorption column (25) at the top.

009837/2219

At the bottom of this column, gaseous ammonia enters through line (26). This gaseous ammonia comes from the separator (15) and is via the line (16) and a compressor (27) brought up. In the compressor, the gaseous ammonia is compressed to a pressure of about 6 at absolute. In the absorption column (25) the compressed ammonia is at a Temperature of 30-35 C absorbed in the liquid. The ones in the column (25) formed liquid is via line (28), pump (29) and line (6) pumped back into the reactor (1).

In the following example, this becomes the described embodiment corresponding material balance is explained in more detail.

example

Every hour the reactor (1) receives a mixture through line (3) from 3.06 kg / 9-methylmercaptopropionaldehyde and 0.89 kg water. Per hour is also 0.85 kg of ammonia through the line (4) and through the line (5) 0.79 kg of hydrogen cyanide introduced into the reactor (1). It is also hourly A mixture of 2.91 kg of ammonia and 1.75 kg of water via line (6) and 0.46 kg of methiononitrile returned to the reactor (1).

2.33 kg of gaseous ammonia per hour are released from the separator (15) discharged via the line (16). From the separator (20) go every hour via line (22) 1.75 kg of water, 0.58 kg of ammonia and 0.46 kg of methionine nitrile away. Furthermore, from this separator via line (21) every hour 3.82 kg of methionine nitrile, 0.35 kg of ammonia and 1.41 kg of water are removed. The methionine nitrile obtained in this way can be in a known manner by means of acid hydrolysis convert into methionine. ·.

009837/2218

Claims (6)

PATENT CLAIMS / l. keri ahren to the production of methionine by means of conversion at over- C ^ / ο atmospheric pressure and a temperature between 0 and 60 C of / 9-Methylmercaptopropionaldehyde with the help of hydrogen cyanide and ammonia or of ammonium cyanide in methionine nitrile using a reaction medium consisting of ammonia and water, followed by Hydrolysis of the methionine nitrile thus obtained in an acidic medium, thereby characterized in that the methionine nitrile-containing reaction mixture obtained in this way is heated in a closed system to a temperature of at most 100 C heated, this reaction mixture then with discharge The released gaseous ammonia expands, the so relaxed reaction mixture under cooling in an ammonia-rich water-rich Liquid layer and a methionine nitrile-rich liquid layer separated, the water-rich liquid layer returned to the process and the methionine-rich liquid layer is subjected to acid hydrolysis. 2. The method according to claim 1, characterized in that «to the temperature increase of the methxononitrile-containing reaction mixture obtained in this way in the closed system in the presence of the reaction mixture formed dissolved amount of ammonia carried out. 3. The method according to claim 1 or 2, characterized in that the accruing gaseous ammonia under pressure in the to be returned water-rich liquid layer dissolves. 4. The method according to any one of claims 1-3, according to the during formation of the methionine nitrile, the temperature is kept between 25 and 45 C and the ammonia: water weight ratio between 1.3: 1 and 2: 1, characterized in that the methionine nitrile-containing reaction mixture in a closed system to a temperature between 65 and 75 ° C. 5. The method according to any one of claims 1-4, characterized in that for Increase in the temperature of the reaction mixture in a closed system this reaction mixture is passed through one or more heated tubes. 6. Methionine or a compound derived therefrom obtained by application of the method according to one of the preceding claims. 009837/2219