DE2236120C3 - Process for the preparation of aminocarboxylic acid alkali metal salts from amino alcohols - Google Patents

Description

The invention relates to an improved process for the preparation of alkali metal salts of aminocarboxylic acids from amino alcohols. It affects in particular the production of alkali metal salts of tertiary aminocarboxylic acids from tertiary amino alcohols.

The synthesis of aminocarboxylic acid alkali metal salts by catalyzed reaction of amino alkanols with alkali metal hydroxides in the aqueous phase is known per se from the publication by Dumas and Stas (Ann. 35, 129-173, 1840). The later ones Work in this area focuses in particular on the conversion of amino alcohols into alkali metal salts under mild conditions, with the result that the amino groups remained largely intact, thereby promoting the conversion into the carboxylic acid alkali metal salts.

DE-OS 18 09 263 discloses a process for the preparation of tertiary aminocarboxylic acid salts known, in which tertiary amino alcohols are reacted with sodium or potassium oxide in the presence of water, cadmium oxide and an accelerator. Of the Accelerator is mandatory. The reaction is preferably carried out in an open vessel, that is at normal pressure.

Furthermore, from US-PS 23 84 817 a process for the oxidation of amino alcohols in Presence of strong alkali and cadmium oxide known. Again, this procedure is performed without compliance carried out a reduced hydrogen partial pressure.

These two processes have the disadvantage that larger or technically meaningful yields can only be achieved by extremely extended reaction times in the range from many hours to several days can be achieved.

The present invention is based on the object of achieving the greatest possible yields of more than 80% of the desired alkali metal salt of aminocarboxylic acid with reaction times of less than two hours

s to get.

It has now been found that in the preparation of alkali metal salts of aminocarboxylic acids from amino alcohols by a process which is based on the Dehydration of amino alcohols is based, an essential lent better time-yield factor achieved thereby can be that an excess over the stoichiometric amount of alkali hydroxide and the presence of at least as much water is provided as is necessary, so that the reaction partners are among the authoritative

is reaction conditions reliably remain in solution, that the presence of a dehydrogenation catalyst is also provided and that the reaction conditions be influenced to the effect that the hydrogen partial pressure in the vapor phase of the reaction space makes up less than 50% of the total pressure

The reaction conditions and the proportions of the batch see a conversion in liquid Phase before, where the proportion of water in the system is more than 25% by weight, based on the total batch, and preferably between 30 and 70% by weight, based on the batch. The amount of sodium hydroxide, based on the amount of aminoalkanol present in the batch before the start of the reaction, must have an excess over the stoichiometric minimum, and is usually in the range between 1.25 to 3 moles per equivalent of aminoalkanol. The catalyst for the oxidation reaction is cadmium, nickel, palladium and / or zinc, preferably a component containing cadmium, hereinafter referred to as "cadmium catalyst" referred to as. In the reaction mixture it is present in an amount that - based on metallic cadmium - generally in the range between 0.2 and 20 gram atom of cadmium per 100 moles of aminoalkanol, and preferably in the range between 1 and 10 grams atom of cadmium per 100 mol of aminoalkanol

With such a composition of the reaction mixture it is achieved that the reaction in liquid phase takes place; the water loss becomes negligible at a minimum or at one kept small value and the reaction temperatures are in the range between 199 ° C and 288 ° C and preferably in the range between 218 ° C and 260 ° C To achieve that the hydrogen partial pressure is less than 50% of the total vapor pressure in the

ίο reaction zone, the pressure conditions would in the reaction zone according to the temperature range in which the reaction is carried out, as a rule between 7.2 atmospheres and 14.4 atmospheres for the lower temperature range and in the range between 303 atmospheres and 101.1 atm for a reaction ^{temperature at 288 0} C kept. The preferred temperature range is between 218 ° C and 260 ⁰ C, pressures in atmospheres usually 14.4 to 17.3 atmospheres gauge for the lower temperature range and atü 27.4 to 38.1 atm are adhered to in the higher temperature range. If the reaction occurs within the specified pressure and temperature range is carried out, it leads to yields within two hours or less of at least 80% of theory.

Although the features of the method according to the invention described above are generally based on the Production of alkali metal salts of aminocarboxylic acids from aminoalkanols can be used,

For the sake of simplicity, the following detailed description of the process is mainly based on the example of the preparation of the trisodium salt the nitrilotriacetic acid described.

Attempts on wetter amino alcohols, e.g. B. at Diethylamine, mono- and dipropanolamine and hexaethanoltriethylenetetramine with an inventive Adjustment of the amount of alkali metal hydroxide with appropriate consideration of the hydrogen to be exchanged for the respective amino alcohols in the respective composition of the reaction mixture have shown that high yields with corresponding Shortened reaction times can be achieved if the conditions according to the invention with regard to water content and hydrogen partial pressure are in the same way be respected.

The dehydrogenation reaction of nitrilotriethanol with an at least stoichiometric amount of sodium hydroxide goes through three stages up to the desired end product, the trisodium salt the trisodium salt, the desired end product is formed. In each of these steps, two moles of hydrogen are exchanged for one mole of sodium; at the same time, each of these process steps is exothermic at higher pressures. As a result, the reaction tends, on the one hand, towards higher temperatures and, on the other hand, towards the release of fairly large amounts of hydrogen. Up to now, the regulation of the temperature has been effected by regulating the reaction rate, ie the slower the reaction takes place, the easier it is to dissipate Ce heat from the exothermic process. at 283 atm to 144.5 atm in the closed system performs The reaction generally tends to drain quickly to the extent as the temperature increases, however it occur more and more production contaminants and other harmful effects when the temperature is above 260 ⁰ C and especially if it rises above approximately 288 ° C

The prior art methods do not suggest that pressure is a reaction parameter It has been found, however, that the hydrogen pressure varies with respect to the Reaction rate and under special conditions also on the yield of the desired Product has a particular effect. B. over 144.5 atü to the fact that they through Cadmium-catalyzed dehydrogenation of triethanolamine with sodium hydroxide inhibited or completely is prevented. However, a low pressure results in a surprising and clearly noticeable one Increase in the rate of reaction, especially when the hydrogen partial pressure in the Reaction system is reduced to the vicinity of practically zero.

In order to achieve the best possible utilization of the plant and the production of nitrilotriacetic acid at the lowest possible cost, the highest possible reaction rate with the necessary selectivity must be sought. According to the invention, this result can be achieved in that hydrogen from the reaction-side part of the system as quickly as it is formed, is removed and in that the Hydrogen partial pressure over the reaction mixture is kept as close to zero as possible. One A measure to achieve this is that the reaction is carried out under reflux conditions is so that the hydrogen formed is quickly removed with the rising solvent, in this case water vapor. The water vapor is condensed and returned to the reaction system to reduce the Maintain water concentration at least at the minimum value described above; the hydrogen is blown off via a corresponding Throttle valve run out of the system. The reflux conditions must be chosen so that a excessive water loss is prevented. The reaction equilibrium of the reaction of alkali metal hydroxides with amino alcohols to form Metal alkoxides and water are well known to the extent that water is removed from the reaction system lets escape, the reaction equilibrium is shifted in the direction of the end products and the constituents necessary to carry out the desired reaction required no longer stay in the system. That more precisely, a reactant has then been removed and the important stoichiometric ratio is no longer given. Replacing the water at periodic intervals allows the reaction to be restarted, but only with one considerable loss of time. Therefore, the total pressure of the reaction system must be selected in this way be that at the desired reaction temperature the water content of the reaction mixture is not less than 1 mole per mole of hydroxyethyl group to be reacted. Such pressures are generally above the 7.2 atmospheric mark.

On the other hand, the hydrogen pressure can usually can advantageously be used to regulate or moderate the reaction rate, e.g. B. in Initial stage of a process working with a very large batch, or during the beginning a continuous process. The initial opportunity to train a very high reaction speed can be dampened by a higher hydrogen partial pressure, at the same time, the risk of a violent temperature surge is also reduced. The heat of reaction can then also be very effective via the The first part of the reaction can be distributed without extensive and subsequently superfluous measures necessary to prevent the temperature from "running away" as a result of an overly rapid reaction process are.

Another advantage of carrying out the process at low hydrogen pressure is the effective use of the cadmium catalyst. It was found that an effective catalyst must appear to be in the form of a soluble cadmium (II) complex. The redox potential of the pair cadmium (II) / Cadmium (O) is so low in the temperature range in which the process is carried out that it is already a relatively low hydrogen pressure is sufficient to reduce cadmium (II) to metal. Within the In the range of process conditions that can be used in practice, hydrogen partial pressures of about 50% of the total vapor pressure in the reaction zone, so all or at least essential part of the cadmium catalyst content can be reduced to the metallic form, which is then in turn is catalytically ineffective. Accordingly, it would turn out to be a continuous process

collect metallic cadmium in the reaction vessel. Although metallic cadmium tends to be in alkaline To go back into solution in the milieu, too high a partial pressure causes the opposite Driving force The metallic stage then represents the equilibrium stage in that it is the cadmium as If, however, the accelerating agent makes ineffective and the sedimentation tendency intensified Hydrogen partial pressure less than 50% of the total pressure the equilibrium shifts from the metallic form of the cadmium in the direction of the Complex. The complex can dissolve in an alkaline environment and intervene in the reaction.

The complex of cadmium-NTA (nitrilotriacetic acid-sodium) is somewhat soluble under the reaction conditions in the aqueous solution of the end product NTA (Na) ₃ = (trisodium nitrilotriacetate), but under normal temperatures it is essentially insoluble and can therefore easily be physically Routes from the final product e.g. B. by filtration, centrifugation od. DgL are deposited.

The cadmitime-NTA-Na complex isolated in this way also has the advantage that it can be returned to the reaction system, where it not only dissolves in the mixture of the aqueous solutions of nitrilotriethanol and alkali hydroxide but also directly with the original cadmium (II) -complex regresses with its apparently fully restored accelerating effect against the conversion of nitrilotriethanol / water / alkali hydroxide into NTA (Na) ₃ .

The examples listed below show the effects of the invention which are advantageous from many respects Procedure. These examples serve more to explain characteristic or exemplary ones Embodiments as the presentation of the scope.

Example 2

On one for continuous procedure at 199 ° C and for continuous removal of hydrogen under controlled pressure conditions certain apparatus would be the storage vessels for the supply of the starting materials in the proportion of three moles of sodium hydroxide and 20-50Mol of water per one mole Nitriloethanol charged The cadmium is used as an oxide in

ίο an amount of 0.05 mole per mole of nitriloethanol admitted. The normally insoluble orange-red solid cadmium oxide dissolves quickly and gives a colorless solution. In order to clearly show the effect of the influence of the hydrogen partial pressure, the Residence time in the reaction zone is set to about five minutes

The general progress of the reaction and the speed of the individual reactions can through Determination of the consumption of sodium hydroxide in the exiting reaction mixture ": be followed. The Influence of the hydrogen pressure on the reaction rate can be seen from the following data which were obtained at a reaction temperature of 199 ° C.

At Pressure*) Partial P _H 2 in % Around Relative sentence pressure % setting **) Reaction H ₂ speed atü atü atü age F. 11.5 0.6 5 11.4 1 G 15.0 3.5 23 8.2 0.7 H 20.8 9.2 44 3.5 0.3

*) Total vapor pressure over the reaction system.
*) Determined by the consumption of sodium hydroxide.

example 1

For example, to run a discontinuous process, an autoclave with a volume of about 3.81 is charged with 300 g of nitrilotriethanol, 300 g of sodium hydroxide (excess 24%), 550 g of water and 15 g of cadmium dioxide Pressure relief valve, which is set to the 28.9 atü, connected and then a hygrometer connected to it. From the point in time at which the first gas escapes or the total pressure of 28.9 atmospheres is reached, to the point in time when 133 liters of gas (= 99% of theory) have escaped, about 80 minutes pass. After cooling to room temperature, water is added up to a total weight of about 1500 g. The insoluble complex of Cd-NTANa is filtered off (dry weight 32 g). After removal of the remaining cadmium by precipitation as sulfide and subsequent filtration, the filtrate is analyzed with the aid of nuclear magnetic resonance spectroscopy using sodium acetate as the standard. The spectrum shows that 97% of the hydroxyethyl groups have been converted into carboxymethyl groups. This corresponds to a utilization of the charge of more than 90% and a yield of NTA (Na) ₃ of 90% (without taking into account the angle that was deposited with the catalyst).

In the aforementioned experiments, the flow rate and concentrations were kept constant. The data listed clearly show the advantage of carrying out the process at a low hydrogen partial pressure and, in conjunction with other relevant observations, justify the striving for a Procedure with hydrogen partial pressures of less than 50% of the total vapor pressure. The for Catalysts useful for this reaction are not limited to being used to begin Initiation for the system depends exclusively on the cadmium (II) complex described above Cadmium in metallic form or a corresponding salt or complex with at least one is also suitable partial and sufficient solubility in the system triethanolamine / alkali hydroxide, in which case an effective Amount of the above-described cadmium (II) complex is formed. Show more metals also have the desired catalytic properties, but not necessarily to the same extent Effectiveness so z. B. nickel, palladium and zinc. While sodium hydroxide is the most suitable However, other alkali and earth metals in the form of their hydroxides are suitable as alkali metal salt. B. Lithium hydroxide, calcium hydroxide, barium hydroxide and potassium hydroxide:; id. Further tests have shown, that reaction times or residence times in the reaction zone in the range between ten minutes and ten Hours are possible, but the best

Results achieved when these times are less than two hours. The preferred response time is no more than thirty minutes.

Example 3

In a nickel-lined, 300 ml autoclave 17.4 g of bishydroxyethylpiperazine, 10 g of sodium hydroxide, 0.5 g of cadmium oxide and 30 g of water were used. After a reaction at 11.5 atmospheres over two hours, the end product - as in Example 1 described - treated and isolated. The one using sodium acetate as the standard substance Analysis performed by nuclear magnetic resonance spectroscopy showed essentially complete conversion of the bishydroxyäthylpiperazine and - based on the bishydroxyäthylpiperazin - a 96.1% yield of disodium salt.

Comparative experiment I

The inhibitory effect of high hydrogen pressures is shown below.

A 300 cc autoclave was charged with 0.5 g of cadmium oxide per 10 g of nitriloethanol, sodium hydroxide and water for each batch. The autoclave was then filled with hydrogen up to the pressure indicated in the table Then, it was heated, the temperature controller was set to 205 ⁰ C. until no further increase in pressure could be observed. Heat development were observed in the mixtures A and B, where the temperature rose briefly above 205 ⁰ C. The reaction products were dissolved in water, filtered and analyzed by evaluating the nuclear magnetic resonance spectrum.

Sowing / Wnsscrslofl- Pressure I'll.-, on Implemented (Time) Together 8th application of the Reaction clock find Triethanol hours Product 76 ain in 100 iitii alü aiii "-" % Mono *.) - % Di *) 7. NTA ***] Λ _ 69.4 57.8 100 > 8 _ - _ 95 B. 28.9 109.8 98.3 100 > T 42 50 C. 57.9 132.9 121.4 100 > 8 16 8th D. 86.7 156.1 144.5 46 > 8 - - E. - 11.5 -0.6 100 1.8 - 95 F. 11.5 11.5 -0.6 100 1.9 - 92

*)% Mono means:% Bishydroxyäthylglycine as sodium salt. **)% Di means:% llydroxiäthyliminodiacetic acid as sodium salt. ***)% NTA means:% nitrilotriacetic acid as sodium salt /.

The batches E and F were heated as comparative experiments according to the conditions of the inventive method in the same manner and with similar Cargenzusätzen in the closed autoclave at 205 ⁰ C, but with the difference that in the Autoklawerschluß a reflux condenser, a pressure regulating valve and in that of A hygrometer was interposed between the line leading away from the pressure regulating valve.

Comparative experiment 2

A copper-lined, approximately 3.8 liter autoclave is charged with 300 g of nitrilotriethanol, 300 g of sodium hydroxide, 425 g of water and 39 g of the crude cadmium-NTA-iNaJ complex from a previous experiment of 23.1 atü and brought to the reaction temperature, the pressure is kept at 23.1 atü with the aid of a proportionally acting pressure control valve. The hydrogen escapes through the pressure control valve and is passed through a hygrometer. The reaction mixture is heated ^{to 218 ° C. for 7 hours.} A total of about 125 I.

jo measured on hydrogen (93% of theory). After this To cool, 857 g of water are added and the mixture is filtered. The catalyst precipitate weighs 31.5 g. The filtrate is then treated with sodium sulfide in order to reduce the remaining traces of cadmium.

Beat 4 ⁷ j, and then analyzed for the content of NTA (Na) ^. The end product consists of 75% NTA (Na) ₃ and 25% IDA (the sodium salt of iminodiacetic acid). From this it can be seen that a process carried out outside of the conditions described leads to a good degree of conversion, but despite> .r extended reaction time leads to an unsatisfactory composition of the end product Water content can be shortened, as shown by the results of further experiments set out in the table below. The total pressure in these tests was 23.1 atm in all cases.

approach 1.) water
G Reaction
temperature 2.) Yield
NTA (Na) ₃ 2.) Yield
IDA (Na) ₂ 1.) g CDO Time
hours A.
B.
C. 600
375
375 205 °
232 °
233 ° 73.6
87.9
89.8 26.4
21.1
10.2 7.5
5.0
8.5 20th
<2
<2

A few runs were made in which the initial charge was made up to the reaction zone was from one part by weight of nitriloethanol, 3 parts by weight of NaOH and 3 parts by weight of water, and a corresponding amount of cadmium catalyst. The overall pressure was throughout the Reactive at a temperature of 250 ° C and at about 27.4 atmospheres, but the escape of the vapor phase was not selectively controlled. The so occurred loss of water from the S / 'item to form a non-liquid cake in the reaction vessel. After removing the cake and his The analysis of the content of the trisodium salt of nitrilotriacetic acid is far from satisfactory Result. Furthermore - regardless of the time, temperature and Printing conditions - no further conversion

TO d?! T! iJPwijnQrhtpn PrnHiilct mphr hpnharhtpt ₍

after the water originally present in the reaction zone had gone away. More attempts show that cake formation occurs even if the desired reaction - at least partially - still continues if the water content in the reaction system is less than 25%, based on is the total weight of the reaction mass. In the same way it has been found that the best feasible process conditions are given when the reaction mass has the consistency of a retains pumpable liquid, which in turn requires that water in an amount of about 40%, based on ■ 5 is the weight of the total reaction mass, is present.

In these and similar tests, it was further observed that: - then, the response speed increases with both the temperature, - annealing temperatures than 260 ⁰ C the desired reaction significantly adversely affect uind that equally clear at about 288 ° C and above, degradation products and unwanted side reactions such as become completely unbearable.

In summary, it can be stated that the process

r, rensweise within the certain limits and especially while maintaining a hydrogen partial pressure less than 50% of the total pressure in the

Rpaklinns7nnp da7ii lead HaR the ffpwünsrhtp

Product can be received in the minimum quantity 2D specified at the beginning and in less than two hours.

So the procedure can take place under similar conditions

can also be continued within reasonably extended periods of time without loss of material either in terms of quantity as well as in terms of

_> -> quality of the end product occur.

Claims (2)

Patent claims: 1. A process for the production of aminocarboxylic acid alkali metal salts of corresponding by reacting at least one primary alcohol group-tasting amino alcohols with an excess over the stoichiometric amount of alkali metal hydroxide in the liquid phase and in a closed reaction space at temperatures between 199 ^C C and 288 ° C in the presence of 25 up to 70% by weight of water and a catalytic one! Amount of cadmium, nickel, palladium and / or zinc, characterized in that one a) removes the mixture of hydrogen and water vapor obtained under these reaction conditions as overhead vapor and passes through a cooler, b) the condensed water is returned to the reaction zone and c) throttles the gas discharge from the cooler to such an extent that there is a pressure in the reaction zone between 7.2 and 101.1 atmospheres, as well as a hydrogen partial pressure of less than 50% of this Pressure is maintained. 2. The method according to claim 1, characterized in that the pressure in atmospheres areas 7.2 to _8: 6 atm atm at 199 ° C and 27.4 to 38.1 atm at 260 ⁰ C holds.