NO136790B - PROCEDURES FOR CONTINUOUS PRODUCTION OF NITRILOTRIACETONITRILE. - Google Patents

Description

The invention relates to a method for particularly continuous production of nitrilotriacetonitrile by reacting an ammonium salt with formaldehyde and hydrocyanic acid in an acidic environment.

Nitrilotriacetonitrile has gained increased importance in recent years and increasingly greater economic interest, as the compound's saponification product, nitrilotriacetonitrile and its salts find extensive use in the detergent industry, textile dyeing and electroplating technology.

According to German patent document no. 694,780, it is known to prepare nitrilotriacetonitrile by mixing a solution of ammonium sulfate in 30% formaldehyde while cooling with concentrated hydrochloric acid, and allowing this, while stirring, to flow into a 24% aqueous sodium cyanide solution. After heating the mixture for 20 hours at 40°C and a further 20 hours at 6o°C, the precipitated nitrilotriacetonitrile can be worked up from the solution. For the production of nitrilotriacetonitrile according to this method, it is important that the reaction mixture is kept acidic during the reaction, as an undesirable discoloration of the reaction mixture occurs in the alkaline range.

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described method of working is only unsatisfactory, as the hydrochloric acid is consumed by the addition of the sodium cyanide to the starting mixture to form common salt and thus the acidity of the solution becomes increasingly less. As a result of too rapidly decreasing acid concentration and possibly a shift in the pH value to the alkaline range, unwanted organic by-products can occur which cause a browning of the reaction mixture. Another disadvantage of the known process is the necessary purification of the process raw product for inorganic salts. To remove the salts, the 2-nitrile triacetonitrile is washed out with water,

whereby part of the nitrile is lost in the wash water together with the salts.

Attempts have been made to overcome these disadvantages by the method according to German patent no. 1,112,081, using hydrocyanic acid instead of sodium cyanide. According to this method, a liquid reaction mixture of equimolar amounts of formaldehyde and liquid or gaseous hydrocyanic acid is reacted at a pH value of <3, preferably <1 with ammonia while maintaining this pH value, so that for each reacted hydrogen atom in the ammonia one mole of formaldehyde and hydrocyanic acid were added, the rate of addition of the ammonia being regulated in such a way that it essentially reacted immediately and completely to nitrilotriacetonitrile, which was then separated as a crystallisate. The required amount of acid for setting the pH, e.g. sulfuric acid, was added to the starting mixture in catalytic amounts.

According to this prescribed method, due to the small amounts of acid, it can hardly be avoided that, in case of local overdose of ammonia, a shift of the pH value in the reaction mixture to the alkaline range occurs, whereby a discoloration of the reaction mixture and contamination of the reaction product is formed. Already at pH values between 2 and 3, clearly detectable amounts of aminodiacetonitrile and methylene-bis-aminodiacetonitrile are formed as by-products, and these compounds turn brown at the reaction temperature used during decomposition and thus impair the product quality of the nitrilotriacetonitrile. In this case, according to German patent no. 1,112,081, it is proposed that the reaction mixture be decolored with charcoal.

The danger of by-product formation can only be avoided when the ammonia is added at a low rate to the starting mixture and one thus expects long reaction times. Both the additional addition of the ayXa-gg-in as mentioned and the low rate of addition of the ammonia must be considered disadvantages of the method. There has thus been a need to find an improved process for the production of nitrilotriacetonitrile which is not affected by these disadvantages and which, secondly, can be adapted to continuous production.

A process for the continuous production of nitrilotriacetonitrile is described in German specification no. 1,805,404. According to this method, at least stoichiometric quantities of ammonia, formaldehyde and hydrogen cyanide are reacted in the presence of a mineral acid at a temperature of over 120°C, especially 125 - 135°C, and a pressure between 0.35 and 7 atmospheres overpressure, and the essentially volatile nitrilotriacetonitrile formed is fed to a quench device for crystallization. A preferred embodiment consists in preparing hexamethylenetetramine by a preliminary reaction from ammonia and formaldehyde, and reacting this with more formaldehyde and hydrocyanic acid to form the nitrile. As regards the residence time for ammonia, formaldehyde and hydrogen cyanide in the reaction vessel, 1-30 minutes is suggested according to this known method.

Despite the short residence time for the reaction mixture in the reactor, with this method, due to the high reaction temperature of over 120°C, it is not possible to avoid unwanted by-products and decomposition products, which are primarily manifested by a yellowing and browning of the process products, and by a partially too clearly unwanted saponification of the nitrile, so that the manufactured product does not have consumer quality. On the other hand, lower temperatures below 100°C, as indicated in German specification 1.805-404, whereby the formation of by-products can at least be reduced, lead to a reduced yield from initially up to 90 and down to approx. 7<3% of the theoretical yield, which means that the process is not economically beneficial.

It was now surprisingly found that the nitrilotriacetonitrile can be produced from an ammonium salt of a non-oxidizing acid, formaldehyde and hydrogen cyanide in a continuous process and with a good yield of more than 90% and with outstanding purity under simultaneously gentle reaction conditions, i.e. at a reaction temperature between 50 and 110°C, when the reaction is carried out in two process steps, i.e. in two reactors connected one after the other.

The invention therefore relates to a process for the continuous production of nitrilotriacetonitrile by reacting an ammonium salt of a non-oxidizing acid with formaldehyde and hydrogen cyanide in an aqueous acidic phase at an elevated temperature and separating the reaction mixture after the reaction has ended while recovering crystalline nitrilotriacetonitrile on the one hand and an aqueous acidic phase such as sodium hydroxide on the other hand, as the method is characterized by continuously adding aqueous solutions of the ammonium salt and formaldehyde to a pre-reactor, the ammonium salt in relation to the formaldehyde being present in a stoichiometric excess of 5 - 40%, and under good thorough mixing ing brings the components to reaction at a temperature of 50 - 110°C and a residence time in the reactor of 2 seconds to 4 minutes, after which the resulting reaction mixture is reacted in a connected reactor with a stoichiometric amount of hydrogen cyanide in an aqueous acidic phase under a pressure of 3 - 25 ato and one to f lysing of the formed nitrilotriacetonitrile sufficient temperature within 3-20 minutes and from the reaction mixture from the post-reaction nitrilotriacetonitrile precipitates on cooling and relaxation to atmospheric pressure and separates from the aqueous phase. The method of the invention is particularly suitable for the continuous production of nitrilotriacetonitrile. In a pre-reactor, aqueous solutions of ammonium salt and formaldehyde are continuously introduced, whereby the ammonium salt is present in a stoichiometric excess of 5 - 40% in relation to the formaldehyde, and is reacted with good mixing of the components at a temperature of 50 - 110°C and a residence time in the reactor of 2 seconds to 4 minutes, after which the reaction mixture is reacted in a downstream reactor with a stoichiometric amount of hydrogen cyanide in aqueous acid phase under a pressure of 3 - 25 ato and a sufficiently high temperature to liquefy the nitrilotriacetonitrile formed, during at least 3 minutes, whereupon the nitrilotriacetonitrile is worked up from the latter reaction mixture by precipitation after cooling and release to atmospheric pressure, and is separated from the "aqueous phase. An approximately saturated aqueous ammonium salt solution and a 20 to 55% by weight aqueous, methanol-free formaldehyde solution are advantageously used, whereby the stoichiometric the excess of ammonium salt, for example, can be 15 - 20% ammonium salts, salts of sulfuric acid, phosphoric acid or hydrochloric acid can especially be used. A particularly favorable modification in terms of low by-product formation is achieved when the temperature in the prereactor is 60 - 70°C and the residence time for the reaction components in this reactor is 1 - 2 minutes.

The reaction in the downstream reactor is preferably carried out with liquid hydrogen cyanide or an aqueous solution of at least 40% by weight, and it is advantageous for the reactor to be operated under a pressure of 10-15 ato and a temperature of 90-110°C. The reaction mixture's residence time in this reactor is not as critical as in the pre-reactor when it comes to the formation of the by-product, but unwanted discoloration of the reaction products from yellow to brown also occurs here with unnecessarily long residence times. To avoid this, a residence time of 3-20 minutes is suggested, especially 6-10 minutes.

For the preparation of nitrilotriacetonitrile, the reaction mixture is drained off after the reaction has finished from the downstream reactor and quenched by simultaneous release to atmospheric pressure to a temperature of 20 - 30°C, whereupon the nitrile precipitates out. The nitrile can be separated by centrifugation or centrifugation of the reaction mixture, after which the nitrile can optionally be washed out with water and dried.

A further feature of the processing is that the surplus of added ammonium salt as well as the released acid that is formed during the process after transfer to the ammonium salt is recovered and fed back into the first reactor. For recovery of excess ammonium salt and liberated acid in the form of ammonium salt, approx. the same volume amount of saturated aqueous ammonium salt solution corresponding to the starting product and evaporates from this mixture in vacuum approx. the same volume of water that is introduced into the reaction process with the output products and is formed as reaction water during the process. The liquid acidic evaporation residue was adjusted with ammonia at a pH of no more than 6, particularly 3 - 5> and the ammonium salt that separated from the evaporation residue was separated and the ammonium salt returned to the pre-reactor after preparation of a corresponding aqueous solution. From the evaporation residue freed of solid ammonium salt, the oily by-products formed by the reaction are separated, and the remaining aqueous phase is introduced into the evaporator together with new mother liquor freed of nitrilotriacetonitrile.

Reactors which are particularly suitable for the invention's pre- and post-reactor method have been shown to be tubes, pipes or plate heat exchangers made of chrome nickel steel, nickel molybdenum alloys or enamelled steel, with specific dimensions. In more detail, the following should also be noted: As already indicated, the residence time in the pre-reactor is an essential feature of the invention, since by maintaining the stated residence time, one affects both the nitrilotriacetonitrile yield and the formation of the by-product. The following table 1 shows e.g. the dependence of the nitrilotri-acetonitrile yield on the residence time of the ammonia salt/formaldehyde mixture in the pre-reactor at an operating temperature of 70°C.

At higher operating temperatures than 70°C works

man with correspondingly shorter residence times and at lower temperatures correspondingly longer residence times. Thus, it was found that at an operating temperature of 95 - 105°C, a residence time of 5 - 10 seconds was sufficient to achieve good NTN yields by subsequent reaction with hydrogen cyanide.

Substantial deviations from the process conditions specified for the pre-reaction, e.g. in terms of operating temperature and residence time, gives poorer NTN yields.

With regard to the reaction in the pre-reactor, it was found with the help of H-NMR spectrum that no urotropin was formed, but that

a reaction took place between ammonium salt and formaldehyde in the molar ratio 1:1, where the degree of reaction is time-, temperature- and concentration-dependent. The yield of nitrilotriacetonitrile depends, after the addition of hydrogen cyanide, on the degree of pre-reaction conversion. A too long residence time for the formalin/ammonium salt mixture, especially at high temperatures, leads to a reductive alkylation of the ammonium ion by the formaldehyde with the formation of methylamine and formic acid.

Depending on the water content of the starting materials, for example aqueous hydrogen cyanide or formaldehyde solution, different concentrations of nitrilotriacetonitrile are obtained in the post-reactor reaction mixture. In order to prevent a premature precipitation of the nitrile from the reaction mixture at a high nitrile concentration and a possible clogging of the reactor, it is necessary to maintain the minimum temperature in the reactor where the reaction mixture remains liquid. In the following table 2, examples of minimum temperatures for different NTN concentrations in the reaction mixture in the post-reactor have been listed.

As the quality deteriorates, especially the color of the reaction product, with increasing temperature, the required minimum temperature should not be significantly exceeded.

The mother liquor that remains after working up the nitrilotriacetonitrile from the reaction mixture contains sulfuric acid as another reaction product, as well as organic by-products such as e.g. glycolic acid nitrile, methylaminodiacetonitrile and methylene-bis-aminodiacetonitrile in a concentration of

1-2 wt. When one per unit weight nitrilotriacetonitrile gets

3 - 4 times as much mother liquor and this not without caveats

nings can be sent to sewers, one must preferably find an economic processing of the mother liquor as an essential component of an NTN production. Various known methods suggest returning the byproduct-containing mother liquors to the reactor after neutralization with ammonia, which must be considered a disadvantage, because there is a build-up of pollutants in the reactor and an increasing discoloration of the reaction products in

for black dyeing. The method proposed here for processing

extraction of the mother liquor must thus be described as progress.

The method of the invention offers advantages in

stick to the known method in particular because it involves a continuous production of nitrilotriacetonitrile with a hitherto unachieved yield under gentle conditions at the same time

els, whereby a clean, non-discolored product is obtained. Furthermore, the processing of by-products and the recovery of starting materials are solved in an economical way.

An example of carrying out the method in

according to the invention is shown in the -attached block diagram,.:n»e.n

however, the invention is not limited to this.

In a pre-reactor 1 surrounded by a heating jacket and e.g. consisting of tubes, an aqueous ammonium sulfate solution is introduced continuously through line 2, and through line 3 an aqueous formaldehyde solution, and after good mixing at a temperature of 50 - 110°C, it reacts during a residence time in the reactor of 2 seconds to 4 minutes. The reaction mixture in the pre-reactor 1 now passes through pipeline 4 to the downstream reactor 5 where, after good mixing, the reaction components are reacted with hydrogen cyanide in an aqueous acid phase under a pressure of 3 to 25 ato and a sufficient temperature for the formed nitrilotriacetonitrile to liquefy, during at least 3 minutes. The hydrogen cyanide is supplied through pipeline 6 to reactor 5, which has the same shape as reactor 1. The recovery of the nitrilotriacetonitrile. from the reaction mixture which is drained off through line 7 takes place in such a way that the reaction mixture is first decompressed in the crystallizer 8 to atmospheric pressure and cooled, whereby the nitrile is poured out of the aqueous phase, and then the precipitate is separated in the apparatus 9, which is connected to the crystallizer 8 through the line 10 , by filtration or centrifugation. The nitrile is taken out through the line 11. The aqueous mother liquor from the separator 9 contains, in addition to excess ammonium sulphate, the sulfuric acid formed, as well as smaller amounts of organic by-products. For recovery of the sulfuric acid and the excess ammonium sulfate, the mother liquor is introduced through lines 12 and 13 together with an equal volume of aqueous saturated ammonium sulfate solution, supplied through line 15, to the evaporator 14 and the mixture is evaporated approx. the same amount of water that is introduced together with the starting materials and that is formed as reaction water. The evaporation takes place in a vacuum. The supply of saturated ammonium sulphate solution to the evaporator only occurs once to facilitate the process, as this solution is supplied to the circuit from the separator 25 through line 13 - The evaporated water is taken out through the evaporator top 14 through line 16 and fed either to the mixing vessel 17 or is partially led out through line 8. The liquid and acidic evaporation residue is led through line 19 to the neutralization vessel 20, and adjusted by adding ammonia via line 21 to a pH value of no more than 6. The sulfuric acid is thereby transferred to ammonium sulfate and precipitated together with the excess of ammonium sulfate introduced to

to begin with, and are separated in the subsequent centrifuge 22

from the aqueous phase and is fed via line 23 back to the mixing vessel 17 for the production of new ammonium sulphate solution

nothing. From the ammonium sulfate-saturated mother liquor after centrifugation, a small amount of oily phase is separated which contains

they keep organic by-products. To separate these, the mother liquor is led through line 24 to the separator 25 - The by-products are drained through line 26 from the separator 25 while the pure mother liquor is led to the evaporator through line 13.

Example 1.

28.75 kg of a 30 wt.g aqueous formalin solution

ning and 18.05 kg of 42 wt.g aqueous ammonium sulphate solution are introduced per hour after heating to 70°C through the wire

2 and 3 to pre-reactor 1. The molar ratio of formaldehyde

and ammonium sulfate was 3 :. 0.6. The temperature in the pre-reactor was 70°C and the pressure approx. 12 ato. The pre-reactor consisted of a heated tube with a diameter of 15 mm, a length of 7.7 m and a volume of 1.36 litres.

For turnover of the starting components, a residence

time of 2 minutes in pre-reactor 1. The reaction mixture from pre-reactor 1 was per hour mixed with 9.7 kg of an 80 wt.g aqueous hydrogen cyanide solution and the mixture then passed through the downstream reactor 5. Reactor 5 also consisted of

is led by a heated tube with a diameter of 15 mm, length 38.5 ra and volume 6.8 1. The temperature in the reactor was 100°C and the pressure approx. 10 ato. Hydrogen cyanide and formaldehyde were present in the reaction mixture in a molar ratio of 1:1. The residence time for this reaction mixture in reactor 5 was approx. 8 minutes. After completion of the reaction, the aqueous reaction mixture from the reactor 5, after prior depressurization to atmospheric pressure, was led to the

water-cooled crystallizer 8 provided with a stirring device, in which there was a crystal mush from the ongoing process, and where the nitrilotriacetonitrile - hereafter called NTN - fell out as a fine crystallisate. In the following separator 9, the nitrile-containing mash was centrifuged. The produced crystalline nitrile can then be washed with water and optionally dried, depending on the desired degree of purity.

The mother liquor from the separator 9, - 43 - 44 kg/hour,

was mixed with a saturated ammonium sulfate solution in molar

kept 1 : 1 and added to the rotary evaporator 14. At 55 - 60°C X)g 120 -■ 150 torr all the water was evaporated here

which was introduced into the process with the starting solutions including the reaction water, a total of approx. 35.5 - 36 kg H20/hour. The sulfur-

acidic concentrate from the evaporator 14 was adjusted in a water-cooled neutralization vessel 20 to pH 3 - 4 with gaseous ammonia while stirring, whereby crystalline ammonium sulphide was formed

barrel and in small quantities a dark brown oily phase. Via centri-

joint 22, the ammonium sulfate was separated from the aqueous solvent

and the oil and dissolved in the mixing vessel 17 with water during

position of a 42 wt.g solution. The solution was

fed to reactor 1. The saturated ammonium sulfate solution from the centrifuge

joint 22 was, after separation of the oil in separator 25, together with the mother liquor from separator 9 returned to the rotary

the steamer 14. The oil, in an amount of 0.6 - 0.8 kg/h, was destroyed.

One got 11.8 - 11.95 kg NTN, in a turnover of

9Q%. The dividend of. NTN was thus 92 - 93% calculated on the added amount of HCN respectively CH20, or 93.8 - 94.9$, calculated on

added hydrogen cyanide and formaldehyde respectively. The NTN product

had a melting point of 128°C.

Example 2.

2.9 kg of a 30% by weight aqueous formaldehyde solvent

ning and i.78 kg of 41.5 wt#-ig aqueous ammonium sulfate solution was per hour after prior heating to 70°C continuously

fed to pre-reactor 1. The molar ratio between formaldehyde and ammonium sulphate was 3:0.58, which gives an ammonium sulphate excess of 16%. Prereactor 1 was likewise heated to a temperature of 70°C. The reactor volume was 134 cm^ and residence

the time in the reactor 2 minutes. The reactor mixture in the pre-reactor 1 was then introduced into the downstream reactor 5 which consisted of a vertical glass tube with a diameter of 45 mm and a height of 700 mm and was provided with a heating jacket, by introduction from below. At the same time, reactor 5 was introduced, where a temperature of

70°C, per hour 0.98 kg 80% by weight aqueous hydrogen cyanide solution

ning, from below. The molar ratio between CH2O and HCN was 1:1. After a residence time in the reactor, the reaction mixture reached

in 8 - 9 minutes a temperature of 75 - 80°C at the upper end of the reactor. The reaction mixture was fed from reactor 5 to two 70°

stirring vessel arranged in cascade, whereby the NTN product fell out immediately

separable from the reaction mixture. After 4 hours, the mixture was taken to the crystallizer 8 where it was cooled to 12 - 15°C.

The NTN crystallisate was separated, washed with water and dried.

The mother liquor was worked up as indicated in example 1 after separation of the crystallisate.

With a turnover of 97 - 98% HCN or CH20, you got per hour 1.2 kg colorless NTN with melting point 128°C. This corresponds to a yield of 92.5%, calculated on the added amount of HCN, respectively CH20, or 94.3 - 95.4%, calculated on the added amount of HCN, respectively CH20.

Example 3-

The procedure was the same as in example 2, but with the pre-reactor

1 volume by reacting formaldehyde with ammonium sulphate var

67 cm^, and one operated with a residence time of 1 minute. The yield was 1.165 kg NTN/hour, or 90%, calculated on the added amount of CH20 or HCN.

Example 4.

The procedure was as in example 2, but the volume of the pre-reactor was 201 cm^ and the residence time 3 minutes. The yield was 1,160 kg NTN/hour or 89>5%> calculated on the added amount of CH20 and HCN respectively.

Example 5-

The procedure was as in example 2, but the volume of the pre-reactor was 335 cm-', and a residence time of 5 minutes was obtained. The yield was 1,140 kg NTN/hour or 88%, calculated on the added amount of CH20 and HCN.

Example 6. (Comparison example):

The yellow-coloured sulfuric acid mother liquor was, in an amount of 4.35 kg/hour, after separation of NTN crystallisate as stated in example 2, with a color number of 2 - 3 according to the Gardner scale, introduced into an evaporator at approx. 70°C and pressure 200 torr, and concentrated by evaporation of water, then with ammonia adjusted to pH 3 - 4 and fed to the pre-reactor in an amount of 1.78 kg/hour for reaction with formaldehyde. Analogously to example 2, the reaction mixture from the pre-reactor was reacted with hydrogen cyanide to form 1.21 kg/hour of colorless NTN. The NTN yield was 93>4%, calculated on the amount of formaldehyde added.

In the circulation process for the mother liquor as described, an admittedly dark-colored mother liquor with color number 5 was again obtained, from which a dark brown oil separated upon neutralization with NH-j. This method shows that a continuous circulation of the mother liquor without a particular purification process is a disadvantage, as by-products constantly accumulate and lead to a

contamination and discoloration of the products.

Example 7-

From a storage container that absorbed 30% by weight

formalin and 96% sulfuric acid in a weight ratio of 29:5.92, 34.9 kg/hour was continuously introduced with a dosing pump, and after cooling to 12°C this solution was taken to a mixing chamber under a pressure of approx. 15 ato. At the same time, 1.97 kg/hour of liquid ammonia was added to the mixing chamber at such a high rate that a molar ratio between NH^ and E^ SO^ of 1 : 0.5 was maintained. The reaction mixture heated up to approx. 100°C. After a residence time of 3 seconds, the mixture was cooled rapidly, within 5 seconds, by flow through a cooling tube,

to approx. 45°C. At this temperature, the reaction mixture passed through the pre-reactor with a residence time of 1.3 minutes.

An 80% by weight aqueous hydrogen anide solution was then added at such a high rate that a molar ratio between CH20 and HCN of 1:1 was maintained (9.8 kg of 80% HCN/

hour). The reaction mixture was now passed through the second reactor consisting of a heated tube with a diameter of 15 mm and a length of 38.5 ni, where the conversion to NTN took place during a residence time of 9.5 minutes, a temperature of 105°C and a pressure of

12 ato. Under the specified conditions, NTN remained in dissolved form until

stand in the mother liquor. The pressure in the tube was maintained by means of a pressure nozzle placed at one end. After this nozzle, the reaction mixture was introduced into a water-cooled stirrer

container as a crystallizer, and brought down to atmospheric pressure,

in which there was a crystal slurry from the ongoing process which maintained a temperature of 20°C, and crystalline NTN precipitated out. At intervals, approx. every 30 minutes, based on the crystallization

tore an amount which corresponded to the introduced amount during this time and worked up the crystallisate. The secreted NTN was washed with water and dried at 70°C to determine the

changed. With a turnover of HCN or CH20 of 97%, you got per hour 11.85 colorless NTN (melting point: 128°C). This

gives a yield of 91.5%, calculated on added amount of HCN respectively CH20 or 94.4%, calculated on converted HCN respectively CH20.

Example 8. (Comparison example).

The procedure was as in example 7, but the formalin and sulfuric acid mixture was heated to 70°C before entering the mixing chamber. Furthermore, the mixing chamber and the mixture were heated with hot water to 70°C in the subsequent residence stretch. This resulted in a temperature in the mixing chamber when ammonia was supplied of approx. 160 - 170°C. The yield of NTN was 7.25 kg/hour or 56%.

With the help of H-NMR spectroscopy, clear amounts of methylaminodiacetonitrile could be determined in the mother liquor.

The extraction of methylaminodiacetonitrile with methylene chloride and subsequent gas chromatographic determination showed that 2.76 kg per hour of this compound, i.e. 35%, calculated on added formaldehyde.

Claims (6)

1. Process for the continuous production of nitrilotriacetonitrile by reacting an ammonium salt of a non-oxidizing acid with formaldehyde and hydrogen cyanide in an aqueous acidic phase at an elevated temperature and separating the reaction mixture after the reaction has ended while recovering crystalline nitrilotriacetonitrile on the one hand and an aqueous acidic phase as mother liquor on the other hand, characterized by continuously adding aqueous solutions of the ammonium salt and the formaldehyde to a pre-reactor, the ammonium salt in relation to the formaldehyde being present in a stoichiometric excess of 5 - 40%, and during good thorough mixing the components bring a temperature of 50 - 110°C and a residence time in the reactor of 2 seconds to 4 minutes for reaction, after which the resulting reaction mixture is reacted in a downstream reactor with a stoichiometric amount of hydrogen cyanide in an aqueous acidic phase under a pressure of 3 - 25 ato and a to flow termination of the formed nitrilotriacetonitrile sufficient temperature within 3 - 20 minutes and from the reaction mixture from the post-reaction, nitrilotriacetonitrile precipitates upon cooling and relaxation to atmospheric pressure and separates from the aqueous phase. 2. Method as stated in claim 1, characterized in that a stoichiometric excess of ammonium salt of 15 - 20% is used. 3. Method as stated in claims 1-2, characterized in that the reaction temperature in the pre-reactor is 60 - 70°C. 4. Method as stated in claims 1-3, characterized in that the residence time for the reaction components in the pre-reactor is 1 - 2 minutes. 5. Method as stated in claims 1-4, characterized in that the reaction with hydrogen cyanide takes place under a pressure of 10 - 15 ato. 6. Method as stated in claims 1-5, characterized in that the reaction with hydrogen cyanide is carried out at a temperature of 90 - 110°C.