WO2005007617A1

WO2005007617A1 - Method for reducing the formaldehyde and cyanide contents in solutions of sarcosine salts

Info

Publication number: WO2005007617A1
Application number: PCT/EP2004/007390
Authority: WO
Inventors: Franz Thalhammer; Hans-Peter Krimmer
Original assignee: Degussa Ag
Priority date: 2003-07-11
Filing date: 2004-07-06
Publication date: 2005-01-27
Also published as: CN1823035A; EP1644317A1; DE10331481A1

Abstract

The invention relates to a method for reducing the formaldehyde and/or cyanide contents in technically produced solutions of sarcosine salts. According to said method, the starting solution is subjected to a thermal treatment such that: a1) the starting solution is brought to temperatures between 20 and 120 °C for an approximately equimolar ratio of formaldehyde and cyanide constituents between 1:0.9 and 1.1, or a2) said solution is heated to temperatures between 120 and 200 °C for a non-equimolar ratio of the formaldehyde and cyanide constituents, and b) the solution is then cooled. The starting solution is adjusted to an approximately equimolar ratio, whereby formaldehyde contents <50 ppm and cyanide contents <10 ppm are obtained in the sarcosinate solutions, by adding calculated quantities of formaldehyde or cyanide. Advantageously, other educts such as methylamine, and/or by-products such as ammonia, can be separated by distillation, before or during the thermal treatment for reducing the formaldehyde or cyanide contents.

Description

Process for reducing formaldehyde and cyanide levels in sarcosine salt solutions

description

The present invention relates to a process for reducing the formaldehyde and cyanide contents in industrially produced solutions of salts of sarcosine (sarcosinates).

Sarcosinates are currently mainly produced by the so-called Strecker synthesis from the starting compounds formaldehyde, hydrocyanic acid and methylamine, with the intermediate sarcosinitrile being subjected to hydrolysis with the aid of alkali metal hydroxide solution in a final process step (see e.g. DE-PS 25 03 582).

Depending on the selected stoichiometric ratios of the starting compounds used, residual amounts of individual starting materials remain in the resulting sarcosinate solution. While excess methylamine and the amounts of ammonia released during the hydrolysis can be completely removed by distillation according to the prior art, the starting compounds cyanide or formaldehyde largely remain in the product in the event that hydrocyanic acid or formaldehyde is not used equimolarly under the process conditions were.

In order to allow the last two starting compounds mentioned to react in the product down to the lower ppm range, both would have to be used in exactly the same stoichiometry, but this is extremely difficult from a process engineering point of view and is therefore also cost-intensive.

Surprisingly, cyanide and formaldehyde have also proven to be very stable in a strongly alkaline sodium sarcosinate solution, although they do not decompose sufficiently even under boiling conditions that are maintained for several hours. Due to its toxicity, cyanide is often used in such deficiency in amounts that formaldehyde remains in the resulting sodium sarcosinate solution and a residual content is accepted, which in technical samples can sometimes be well over 1,000 ppm. With small fluctuations in the metered quantities, batches with high residual cyanide contents can also be obtained.

The product sodium sarcosinate is mainly used for the production of detergents in the detergent sector. However, it is currently of great and increasing importance as a raw material for the production of creatine, which in turn is used as a food supplement (cf. for example EP-A 751 122).

For the latter application, a quality is required that contains formaldehyde impurities well below the values mentioned above. The cyanide content should also be in the range <10 ppm.

From the disadvantages of the prior art described with regard to the required and actual residual amounts of starting compounds, the object of the present invention is to provide a simple process for reducing the formaldehyde and / or cyanide contents in industrially produced sarcosinate-containing solutions. In particular, the qualities of the sarcosinate solutions obtained in this way are intended to be suitable for creatine production. Furthermore, the method should also enable the preparation of other commercial sarcosinate solutions.

This problem was solved with a method in which a sarcosinate starting solution is subjected to a thermal treatment, whereby it a1) at an approximately equimolar ratio of the formaldehyde and cyanide components from 1: 0.9 to 1.1 to temperatures between 20 and 120 ° C., or a2) at a non-equimolar ratio of the formaldehyde and cyanide components Components is heated to temperatures between 120 and 200 ° C, and b) finally cooled.

Surprisingly, it has been shown that under the selected process conditions a1) and / or a2) the decomposition of the impurities cyanide or formaldehyde increases significantly, but at the same time the actual valuable substance, sarcosinate, remains stable in the solution obtained. In particular, it could not have been foreseen that, in order to accelerate the decomposition, especially at low process temperatures, sodium cyanide can be added in the presence of formaldehyde residues in the product solution in a stoichiometry that is the same as that of formaldehyde - and vice versa. A process temperature which is only slightly above the usual room temperature is sufficient. The degradation of the contaminants can be followed analytically.

It was also found that both cyanide and formaldehyde residues are rapidly degraded if the aqueous sarcosinate solution is heated to temperatures> 120 ° C. In particular, this was not to be expected because - as already explained - an astonishing stability in sarcosinate solutions is known with regard to cyanide and formaldehyde. The course of the known Cannizarro reaction does not take place quickly enough, even under boiling conditions of approx. 105 to 110 ° C, to sufficiently remove formaldehyde. Usually, the thermally induced hydrolysis of cyanide under alkaline conditions, as is known, for example, from the detoxification of waste water, does not succeed in the sarcosinate solution sufficiently fast.

The advantages of this new process were not foreseeable to this extent.

As already mentioned, the method according to the invention is mainly aimed at the purification of solutions containing sodium sarcosinate. However, other types of sarcosinate solutions can also be purified, e.g. other alkali metal sarcosinate solutions or alkaline earth metal sarcosinate solutions. In the context of the present invention, the duration of the thermal treatment is preferably 1 to 300 minutes and particularly preferably 40 to 60 minutes.

It has also proven to be advantageous if, in the case of process step a1), the starting solution is adjusted to an approximately equimolar ratio of these two compounds by adding calculated amounts of formaldehyde or cyanide. After this approximately aquimolar ratio has been set, the impurities are largely and rapidly broken down.

It can also be advantageous here if the calculated amount of formaldehyde or cyanide is added in the form of an aqueous solution in process step a1), which the present invention also takes into account.

With regard to the process temperature, temperatures of the starting solution which are between 60 and 110 ° C. and particularly preferably between 90 and 105 ° C. have been found to be particularly suitable for process step a1).

For the alternative first method step a2), a temperature range between 140 and 170 ° C. is to be regarded as particularly preferred, the present method preferably under pressure conditions Ratios ≤10 bar can be carried out.

According to the task, aims to provide sarcosinate solutions that are suitable for creatine production. For this reason, among other things, the present invention also includes a process variant in which the formaldehyde content is reduced to values <50 ppm and the cyanide content to values <10 ppm. The process is particularly successfully carried out in a 40% by weight sarcosinate solution.

Since the starting solutions can also contain other educts or by-products in addition to formaldehyde and cyanide, educts such as e.g. Methylamine, and / or by-products such as e.g. Ammonia, are separated from the starting solution by distillation.

The preferred embodiments of the present method can be described as follows:

A commercially available sodium sarcosinate solution obtained with the aid of the Strecker synthesis and containing residues of formaldehyde or cyanide is heated to a temperature of 120 to 200 ° C. under pressure conditions, which can be carried out batchwise in a reactor or continuously in a residence time container. both of which should be made of alkali-resistant materials. After a residence time of ideally 40 to 60 minutes, the mixture is cooled.

Alternatively, in the case of analytically determined levels of contamination with formaldehyde or sodium cyanide, the other of the two compounds can be added in such an amount that an almost equimolar ratio of 1: 0.9-1.1 results. The mixture is then heated to 60 to 110 ° C. and ideally cooled to 40 to 60 minutes after a dwell time. Even if starting concentrations of> 500 ppm were present with regard to formaldehyde or cyanide, residual contents of <50 ppm of formaldehyde and <10 ppm of cyanide are obtained.

If the intention is to set the concentration of the solution to a predetermined value, the thermal treatment step for the sarcosinate solution can also be carried out with concentration.

Overall, the claimed process economically reduces formaldehyde and cyanide contents in industrially produced sarcosinate-containing solutions to an extent that make the products obtained particularly suitable as a raw material for the production of creatine.

The following examples illustrate the advantages of the method according to the invention.

Examples

Example 1:

A 40% by weight sodium sarcosinate solution with an analytically determined residual cyanide content of 930 ppm was heated to a temperature of 160 ° C. under pressure conditions (approx. 2.0 bar). Samples were taken at certain intervals and the residual cyanide content was analyzed. Table 1 shows the cyanide values obtained. The sodium sarcosinate content remained unchanged.

Table 1: Time (min) 0 30 60 180 cyanide content (ppm) 930 33 <5 <5 Example 2:

A 40% by weight solution of sodium sarcosinate with an analytically determined residual content of 900 ppm formaldehyde was heated to 160 ° C. in a batch process under pressure conditions (approx. 2.0 bar) and the degradation of the formaldehyde was monitored in samples taken as a function of time. Table 2 shows the values obtained.

Table 2:

Example 3:

100 g of a 40% Na sarcosinate solution with an analytically determined cyanide content of 760 ppm were mixed with the amount of 30% formaldehyde calculated according to Formula 1 at room temperature.

Formula 1 :

B FA

B ', CN

B requirement [g]

CN cyanide

FA formaldehyde

SL sarcosinate solution

M mass

MM Molar mass [g / mol]

Concentration concentration [% by weight]

G content in the sarcosinate solution [g / kg] 0.76 * 0.1 * 31.0 * 100 B FA 0.302 g 26.0 * 30

This solution was heated to reflux (108 ° C.) at normal pressure and analyzed analytically as a function of time.

Table 3:

Example 4:

100 g of a 40% sodium sarcosinate solution with an analytically determined content of 929 ppm formaldehyde were mixed with the amount of cyanide calculated as formula 1 (as NaCN solution; 15.9% by weight with respect to CN).

0.929 * 0.1 * 26.0 * 100 B ', CY 0.490 g 31.0 * 15.9

The solution was stirred and analyzed in parallel at room temperature (I) for 24 h and on the other hand (II) at reflux temperature (108 ° C). Table 4:

Claims

Expectations

1. A process for reducing the formaldehyde and / or cyanide contents in industrially produced solutions of sarcosine salts, characterized in that the starting solution is subjected to a thermal treatment in such a way that it a1) at an approximately aquimolar ratio of formaldehyde and cyanide -Components of 1: 0.9 to 1.1 is set to temperatures between 20 and 120 ° C, or a2) is heated to temperatures between 120 and 200 ° C at a non-equimolar ratio of the formaldehyde and cyanide components and b) is finally cooled.

2. The method according to claim 1, characterized in that the duration of the thermal treatment is 1 to 300 minute (s) and particularly preferably 40 to 60 minutes.

3. The method according to any one of claims 1 or 2, characterized in that in case a1) the starting solution is adjusted to an approximately equimolar ratio of these two compounds by adding calculated amounts of formaldehyde or cyanide.

4. The method according to claim 3, characterized in that in case a1) the calculated amount of formaldehyde or cyanide is added in the form of an aqueous solution.

5. The method according to any one of claims 1 to 4, characterized in that the starting solution in case a1) is set to temperatures between 60 and 110 ° C and particularly preferably 90 to 105 ° C.

6. The method according to any one of claims 1 to 4, characterized in that the starting solution in case a2) is heated to temperatures between 140 and 170 ° C.

7. The method according to any one of claims 1 to 6, characterized in that it is carried out in the case a2) under pressure conditions <10 bar.

8. The method according to any one of claims 1 to 7, characterized in that the formaldehyde content is reduced to values <50 ppm and the cyanide contents to values <10 ppm, particularly preferably in a 40% by weight sarcosinate solution ,

9. The method according to any one of claims 1 to 8, characterized in that before or during the thermal treatment according to a1) or a2) educts, such as. Methylamine, and / or by-products such as e.g. Ammonia, were separated from the starting solution by distillation.

10. The method according to any one of claims 1 to 10, characterized in that the sarcosinate solution treated according to a1) or a2) is used as a raw material for the production of creatine.