Stable methylglycine-n,n-diacetic acid compositions, methods of making and uses thereof

Abstract

The application discloses a storage-stable methyl glycine-N, N-diethylnitrile composition, which contains 5.0-40.0 wt% methyl glycine-N, N-diethylnitrile, 0.1-5.0 wt% sodium or potassium ions, 0.1-1.5 wt% methanol or ethanol, 0.05-0.5 wt% hydrocyanic acid, 0.05-0.5 wt% hydroxyacetonitrile, and the rest is water, and has a pH of 2.0-4.5 tested at 20 DEG C and a Hazen color number of 10-350. The application also discloses a preparation method of the composition and the use of the composition as storage-stable methyl glycine-N, N-diethylnitrile. The composition of the application can be stored for up to 4 months at a storage temperature of 0 DEG C-50 DEG C, and the synthesis of an MGDA product by using the composition has no obvious difference from an existing process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of organic chemical industry, in particular to a methyl glycine-N, N-diacetonitrile mixture with good storage stability, more particularly to a method for preparing the mixture by using hydrocyanic acid, formaldehyde and alpha-alanine, and the use of the mixture in preparing methyl glycine-N, N-diacetic acid and methyl glycine-N, N-diacetic acid trisodium or tripotassium salt. BACKGROUND

[0002] Methyl glycine-N, N-diacetic acid, abbreviated as MGDA, is a small molecule green chelating agent, non-toxic and biodegradable, which meets the OECD standard. MGDA can form 1:1 ligand compounds with common metal ions, has a wide applicable pH range (2-13.5), strong chelating ability and high efficiency, and has superior toxicological safety and biological biodegradability. It is the best choice of aminopolycarboxylic acid complexing agent, and has attracted the attention of the cleaning industry in recent years. Commercial products are mostly solutions or solid products of MGDA or MGDA·3Na.

[0003] In the existing industrialization technology, MGDA is prepared by a hydrocyanic acid synthesis route, which needs to prepare methyl glycine-N, N-diacetonitrile and other nitrile intermediates. In order to obtain high yield and high purity of MGDA, methyl glycine nitrile diacetonitrile (MGDN), methyl glycine-N, N-diacetonitrile (ADAN) and other intermediates often need to be separated, purified by crystallization process, or directly used as intermediate raw materials, which cannot be stored for a long time. The stable storage time is only a few hours, at most a few days. The unseparated unstable intermediate raw materials have many by-products, and affect the subsequent MGDA synthesis yield.

[0004] WO9429421A first discloses a Strecker reaction route using alanine, hydrocyanic acid and formaldehyde as raw materials to prepare MGDA chelating agent.

[0005] US5817864B uses alanine, 30% formaldehyde and 33% sodium cyanide to react in an alkaline medium with a pH value of 10-12. The intermediate is not separated, and MGDA·3Na is directly obtained by hydrolysis and deamination. This synthesis route has more by-products, lower selectivity of MGDA·3Na, and the product is not easy to purify, and the residual amount of impurities such as nitrilotriacetic acid (NTA) is high.

[0006] US5849950B discloses the preparation of methyl glycine diacetic acid trisodium salt using alanine, propiolitrile as raw materials, reacting with formaldehyde and refined hydrocyanic acid in strong acid medium, which can obtain high purity methyl glycine diacetic acid trisodium salt product, but the purity of the raw material is required to be high, especially the raw material hydrocyanic acid needs to reach 99%, the content of impurity NTA·3Na is controlled to be less than 0.3%, and the separation purity of the intermediate is required to be high. The intermediate MGDN is separated by crystallization, and the MGDN is introduced into sodium hydroxide solution at 20°C to hydrolyze and prepare MGDA·3Na.

[0007] CN101171232B discloses a method for separating methyl amino acetonitrile-N, N-diacetonitrile from an aqueous crude mixture. In order to achieve a high yield of MGDA, it is ideal to separate MGDN as an intermediate product.

[0008] CN101171226B discloses a method for preparing methyl glycine-N, N-diacetic acid tris(alkali metal) salt with low content of by-products. The method uses pure methyl glycine cyanhydrin diacetonitrile MGDN after separation to prepare methyl glycine diacetic acid trisodium salt by alkaline step-by-step hydrolysis. The high-purity MGDN is hydrolyzed under optimal conditions, and the content of NTA is controlled to be less than 0.1%.

[0009] CN102993034B discloses a method for preparing imino diacetonitrile solution by hydroxy acetonitrile and ammonia, and preparing methyl glycine cyanhydrin diacetonitrile crystals by reacting with crude hydrocyanic acid gas and acetaldehyde solution. Similarly, strong acid needs to be adjusted to a strong acid environment for reaction, and the intermediate nitrile needs to be separated by crystallization.

[0010] CN107108476A discloses a crystal of alanine N-acetic acid precursor, a preparation method thereof, and application thereof. The method discloses a variety of raw materials and processes for preparing nitrile intermediates, and differences in properties and solubility of different intermediates.

[0011] CN103476741B and US8802894B disclose a method for preparing methyl glycine-N, N-diacetic acid tris alkali metal salt aqueous solution. The optimized process is used to prepare alanine diacetonitrile in an alkaline medium with a pH value of 9-12. The intermediate cannot be stored and is directly used for the preparation of MGDA·3Na. The yield and impurity control level are improved, but the purity of the raw material needs to be high, and there is no influence of stable storage of the intermediate.

[0012] From the above technologies, the preparation process of MGDA and alkali metal salt thereof is as follows: propiolitrile or alanine is reacted with cyanide and formaldehyde by Strecker reaction, and the product is obtained by hydrolysis, or imino diacetonitrile or imino diacetic acid is reacted with cyanide and acetaldehyde by Strecker reaction, and the product is obtained by hydrolysis. The nitrile intermediate MGDN in the preparation process needs to be crystallized or controlled by parameters for direct hydrolysis, so as to effectively control the by-products and improve the yield.

[0013] From the above prior art and technical development, the process for preparing MGDA inevitably has the problems of residual by-products and instability of intermediates or the need for separation and purification. The main defect in the above method is that the intermediate methyl glycine-N,N-diacetonitrile mixture can only exist stably for a short time, several hours to several days. With the increase of temperature and time, undesirable decomposition or polymerization side reactions will cause the quality of the subsequent product to decrease, or the production method only provides an intermediate that can exist stably for a short time. Some methods through crystallization separation and other ways will lead to the existence of cyanide-containing wastewater or mother liquor, which on the one hand reduces the yield, and on the other hand increases the potential environmental protection cost. SUMMARY

[0014] Therefore, the purpose of the present application is to provide a methyl glycine-N,N-diacetonitrile composition that is well stored stably. The composition is a nitrile mixture that is stored stably for a relatively long time, at least more than 1 month, has low hydrocyanic acid consumption and formaldehyde consumption, and has low color number and control of by-product hydroxyacetonitrile, which is beneficial to the control of by-products in the synthesis of MGDA products.

[0015] Another purpose of the present application is to provide a method for preparing the composition using hydrocyanic acid, formaldehyde and alpha-alanine.

[0016] Still another purpose of the present application is to provide the use of the composition for preparing methyl glycine-N,N-diacetic acid and methyl glycine-N,N-diacetic acid trisodium or tripotassium salt.

[0017] To achieve the above purposes, the present application adopts the following technical solutions:

[0018] A storage-stable methyl glycine-N,N-diacetonitrile composition contains, by weight percentage, 5.0-40.0% methyl glycine-N,N-diacetonitrile, 0.1-5.0% sodium or potassium ions, 0.1-1.5% methanol or ethanol, 0.05-0.5% hydrocyanic acid, 0.05-0.5% hydroxyacetonitrile, and the rest is water; and the composition has a pH of 2.0-4.5 and a Hazen color number of 10-350 under a test condition of 20°C.

[0019] In a preferred embodiment, the storage-stable methyl glycine-N,N-diacetonitrile composition contains, by weight percentage, 8.0-35.0% methyl glycine-N,N-diacetonitrile, 0.1-3.5% sodium or potassium ions, 0.1-0.9% methanol or ethanol, 0.1-0.3% hydrocyanic acid, 0.1-0.3% hydroxyacetonitrile, and the rest is water; and the composition has a pH of 3.0-4.2 and a Hazen color number of 20-280 under a test condition of 20°C.

[0020] In another aspect, the foregoing process for preparing a storage stable methylglycine-N,N- dicyanohydrin composition, comprising the steps of:

[0021] a) adding a formaldehyde solution to a mixed solution of alpha-alanine and an alkali metal salt of alpha-alanine to prepare a pre-mixed reaction solution;

[0022] b) reacting the pre-mixed reaction solution with hydrocyanic acid in the presence of an acidic catalyst or without a catalyst to prepare methylglycine-N,N-dicyanohydrin, and during or after the reaction, controlling the hydrocyanic acid content to be 0.05 to 0.5% by weight, preferably 0.1 to 0.3% by weight, by adding hydrocyanic acid, and controlling the hydroxyacetonitrile content to be 0.05 to 0.5% by weight, preferably 0.1 to 0.3% by weight, by adding hydrocyanic acid;

[0023] c) optionally adjusting the pH to be 2.0 to 4.5, preferably 3.0 to 4.2, during or after the reaction, by adding an acid or a base.

[0024] In a specific embodiment, the alpha-alanine:hydrocyanic acid:formaldehyde:sodium (potassium) hydroxide molar ratio = 1.0:(2.02 to 2.06):(2.01 to 2.05):(0.05 to 0.8).

[0025] In a specific embodiment, the acidic catalyst of step b) is selected from one or more of lactic acid, citric acid, tartaric acid, malic acid, ascorbic acid, acetic acid, succinic acid, and oxalic acid.

[0026] In a specific embodiment, the acid of step c) is an organic acid or an inorganic acid, preferably, the organic acid is selected from any one of lactic acid, citric acid, and acetic acid, and the inorganic acid is selected from sulfuric acid or phosphoric acid; and the base is sodium hydroxide or potassium hydroxide.

[0027] In a specific embodiment, the hydrocyanic acid is derived from synthesis gas by either methanol ammoxidation or methane ammoxidation, and the resulting hydrocyanic acid mixture has a content of 5 to 15% by weight, or the refined liquid hydrocyanic acid synthesized by either process has a content of >99% by weight.

[0028] In another aspect, the use of the foregoing composition or the storage stable methylglycine-N,N-dicyanohydrin composition prepared by the foregoing process for storing methylglycine-N,N-dicyanohydrin.

[0029] wherein the storage stable methylglycine-N,N-dicyanohydrin composition can be stored for at least 1 month, preferably up to 6 months, more preferably up to 4 months, at a storage temperature of 0°C to 50°C, preferably 5°C to 25°C, more preferably 5°C to 18°C.

[0030] In still another aspect, the use of the storage-stable methyl glycine-N,N-diacetic acid nitrile composition of the foregoing composition or the foregoing method for preparing methyl glycine-N,N-diacetic acid trisodium salt and / or methyl glycine-N,N-diacetic acid tripotassium salt.

[0031] In still another aspect, the use of the storage-stable methyl glycine-N,N-diacetic acid nitrile composition of the foregoing composition or the foregoing method for preparing methyl glycine-N,N-diacetic acid.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] 1) The storage-stability of the methyl glycine-N,N-diacetic acid nitrile composition of the present application is high, and the storage period of the aqueous solution of the composition is from 1 month to 4 months, which is much better than the prior art that can only be stored for a few days, and the change of the color number with time is also within the control range.

[0034] 2) The composition of the present application can be stored for up to 4 months at a storage temperature of 0°C to 50°C, and can be used to prepare methyl glycine-N,N-diacetic acid and methyl glycine-N,N-diacetic acid trisodium or tripotassium salt, etc., and the synthesis of the MGDA product using the composition has no obvious difference from the prior art. DETAILED DESCRIPTION

[0035] In order to better understand the technical solutions of the present application, the following examples will further illustrate the method provided by the present application, but the present application is not limited to the listed examples, and any other known changes within the scope of the claims of the present application should also be included.

[0036] The storage-stable methyl glycine-N,N-diacetic acid nitrile composition of the present application contains 5.0-40.0 wt% methyl glycine-N,N-diacetic acid nitrile, 0.1-5.0 wt% sodium or potassium ions, 0.1-1.5 wt% methanol or ethanol, 0.05-0.5 wt% hydrocyanic acid, 0.05-0.5 wt% hydroxyacetonitrile, and the balance is water 59.7-87.5 wt%, and has a pH of 2.0-4.5 tested at 20°C, and a Hazen color number of 10-350.

[0037] The storage-stability of the composition containing the above-mentioned composition of the present application of methyl glycine-N,N-diacetic acid nitrile is high, which has the parameters of the control range of the hydrocyanic acid, hydroxyacetonitrile, water, pH, etc. of the present application, and the storage period of the aqueous solution of the composition is from 1 month to 4 months, and the longest can reach 6 months, and the change of the color number with time is also within the control range.

[0038] The storage temperature is 0-50°C, preferably 5-25°C, most preferably 5-18°C, for a storage period of up to 6 months, preferably up to 4 months.

[0039] The above method achieves a 120-day storage stability. Investigation and research show that the composition of methylglycine-N,N-diacetonitrile can be determined by analysis to observe changes in methylglycine-N,N-diacetonitrile and subsequent synthesis of MGDA products, test MGDA product indicators, yield and byproduct impurity content, the main methylglycine-N,N-diacetonitrile decomposition and loss amount is <0.3 wt%, which is significantly improved compared to the yield of the nitrile intermediate of the prior art crystallization, and there is no significant difference in the quality indicators of the MGDA synthesized by the prior art. From the subsequent examples and comparative examples, the comparison of the parameters can be seen in detail.

[0040] In a preferred embodiment, the composition containing methylglycine-N,N-diacetonitrile contains 8.0-35.0 wt% methylglycine-N,N-diacetonitrile, 0.1-3.5 wt% sodium or potassium ions, 0.1-0.9 wt% methanol or ethanol, 0.1-0.3 wt% hydrocyanic acid, 0.1-0.3 wt% hydroxyacetonitrile, and the balance is water 64.6-87.0 wt%, and has a pH of 3.0-4.2 at 20°C, and a Hazen color number of 20-280.

[0041] The application of the composition of methylglycine-N,N-diacetonitrile is for subsequent use in the preparation of methylglycine-N,N-diacetic acid trisodium salt and / or methylglycine-N,N-diacetic acid tripotassium salt or for the preparation of methylglycine-N,N-diacetic acid.

[0042] In addition, the preparation method of the composition of methylglycine-N,N-diacetonitrile of the present application is achieved by the following method:

[0043] a) A pre-mixed reaction solution is prepared by adding a formaldehyde solution to a mixed solution of α-alanine and an alkali metal salt of α-alanine.

[0044] The mixed solution of α-alanine and an alkali metal salt of α-alanine of the present application is prepared by mixing solid α-alanine, water and a base, wherein the base is preferably one or more of sodium hydroxide, potassium hydroxide and potassium carbonate, and the base can be provided in solid form or in aqueous solution, for example, at a concentration of 30-50 wt%. In the present application, the alkali metal salt of α-alanine is the reaction product of α-alanine and a base, specifically sodium α-alanine or potassium α-alanine.

[0045] The alpha-alanine of the present application is not limited in technical source (for example, chemical method, fermentation method, enzyme method), and the raw material is selected from one or more of L-alpha-alanine, D, L-alpha-alanine, D-alpha-alanine, alpha-alanine sodium salt or potassium salt.

[0046] The solubility of single alpha-alanine in water is limited, and the content of alpha-alanine in the aqueous solution of alpha-alanine is less than 18% by weight at room temperature, and the pH value of the solution after dissolution is about 6. By adding part of the lye, a mixed solution is prepared, and there are at least two favorable factors. One is that the initial content of alpha-alanine in the mixed solution of alpha-alanine and alkali metal salt of alpha-alanine can be significantly increased to 40% by weight, and the initial concentration of alpha-alanine is preferably adjusted to 8-40% by weight. The second is that the pH value of the raw material system can also be adjusted to 6-12, and the molar ratio of alpha-alanine to lye (sodium or potassium ion) is 1:(0.05-0.8), for example, including but not limited to 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8.

[0047] The temperature is controlled at 20-35°C, and a pre-mixed reaction solution is prepared by slowly adding a formaldehyde solution in the mixed solution of alpha-alanine and alkali metal salt of alpha-alanine, and the molar ratio of alpha-alanine to formaldehyde is preferably 1:(2.01-2.05), for example, including but not limited to 1:2.01, 1:2.02, 1:2.03, 1:2.04, 1:2.05.

[0048] The concentration of the formaldehyde solution of the present application is 30-50% by weight, for example, 30% by weight, 37% by weight, 44% by weight, 50% by weight.

[0049] Due to process differences, different proportions of methanol are contained in the raw material formaldehyde in the industrial formaldehyde raw material solution, and the methanol content can be controlled by the raw material index. For the methanol or ethanol content of the methyl glycine-N,N-diacetonitrile mixture, the methanol content in the formaldehyde is controlled or the methanol or ethanol is supplemented during the reaction or after the reaction.

[0050] The 5.0-40.0% by weight methyl glycine-N,N-diacetonitrile of the present application contains 0.1-1.5% by weight methanol or ethanol, and the 8.0-35.0% by weight methyl glycine-N,N-diacetonitrile contains 0.1-0.9% by weight methanol or ethanol.

[0051] b) In the presence of an acidic catalyst or without a catalyst, the pre-mixed reaction solution is reacted with hydrocyanic acid to prepare a nitrile, and during the reaction or after the reaction, the hydrocyanic acid content is set to 0.05-0.5% by weight by adding hydrocyanic acid, and the hydroxyacetonitrile content is set to 0.05-0.5% by weight by adding hydrocyanic acid.

[0052] The molar ratio of alpha-alanine: hydrocyanic acid according to the present application is 1.0: (2.0-2.1), for example including but not limited to 1:2.01, 1:2.02, 1:2.03, 1:2.04, 1:2.05, 1:2.06, 1:2.07, 1:2.08, 1:2.09, and preferably the molar ratio is 2.02-2.06.

[0053] The hydrocyanic acid source according to the present application is prepared by methods known in the art, preferably synthesis gas of the methanol ammonia oxidation method or the methane ammonia oxidation method, which is subjected to deamination treatment by an acid washing tower to obtain a hydrocyanic acid mixed gas content of 5-15% by weight, or any known process to synthesize refined liquid hydrocyanic acid content >99% by weight.

[0054] For the present application, in order to achieve high selectivity and high yield of methyl glycine-N,N-diacetonitrile, and the stability of the nitrile mixture, both hydrocyanic acid and formaldehyde raw materials are used in a slightly excessive state, but excessive use inevitably leads to the formation of trace amounts of hydroxyacetonitrile and subsequent side reactions, and at the same time, due to the existence of the reversible reaction of methyl glycine-N,N-diacetonitrile in the reaction process, the existence of slightly excessive hydrocyanic acid and hydroxyacetonitrile is a favorable factor for the stable storage of the methyl glycine-N,N-diacetonitrile mixture for a long time, preventing the reaction equilibrium from being broken and the nitrile product from decomposing into raw materials such as hydrocyanic acid, formaldehyde, and alanine.

[0055] The pre-mixed reaction liquid according to the present application can be reacted with hydrocyanic acid using a single-stage tank reactor with mechanical stirring, or a multi-stage series tank reactor, or a multi-stage series overflow reaction, or a loop reactor, or a tower reactor for gas-liquid contact (plate tower, packed bed tower, bubble bed tower, etc.).

[0056] In the absence of a catalyst, methyl glycine-N,N-diacetonitrile can be prepared by reacting alpha-alanine and an alkali metal salt solution of alpha-alanine in an initial alkaline environment with pH 9-11, adding formaldehyde and hydrocyanic acid in an alkaline environment, gradually reducing the pH of the reaction system by the acidity of hydrocyanic acid itself or by adding acidic substances, and the initial alkaline environment can improve the reaction efficiency, but the risk is that when the addition speed of hydrocyanic acid is too fast, the content of hydroxyacetonitrile formed by hydrocyanic acid and formaldehyde in the alkaline catalytic environment will be high, and too strong alkalinity is also not conducive to the stable existence of the formed hydroxyacetonitrile and intermediate product methyl glycine-N,N-diacetonitrile, and the operation flexibility is small, and it is necessary to control the material addition rate and reaction parameters more accurately, and the preferred scheme can introduce amine additives to reduce the existence of trace amounts of hydroxyacetonitrile in the system, and also reduce the possibility of polymerization and side reactions. During or after the reaction, the content of hydrocyanic acid is set to 0.05-0.5% by weight, and the content of hydroxyacetonitrile is 0.05-0.5% by weight, which is conducive to the stability of the nitrile mixture.

[0057] In another preferred embodiment, the pre-mixed reaction solution is reacted with hydrocyanic acid in the presence of an acidic catalyst to produce a nitrile, and during or after the reaction, the hydrocyanic acid content is set to 0.05-0.5% by weight by adding hydrocyanic acid, and the hydroxyacetonitrile content is set to 0.05-0.5% by weight by adding hydrocyanic acid, preferably the hydrocyanic acid content is set to 0.1-0.3% by weight by adding hydrocyanic acid, and preferably the hydroxyacetonitrile content is set to 0.1-0.3% by weight by adding hydrocyanic acid.

[0058] The acidic catalysts described in the present application are one or more of lactic acid, citric acid, tartaric acid, malic acid, ascorbic acid, acetic acid, succinic acid, and oxalic acid.

[0059] The process for preparing methylglycine-N,N-diacetonitrile described in the present application can also be carried out in an acidic environment, with the pH of the system controlled to be 2.0-4.5, and preferably in a weakly acidic environment with the pH controlled to be 3.0-4.2. A weakly acidic environment is beneficial in that it is conducive to the stability of the raw material hydrocyanic acid and the nitrile intermediates in the product or by-products, and it also slows the rate of generation of unnecessary by-products and the accumulation of their concentrations, which is conducive to the addition of hydrocyanic acid to the system and the presence of lower concentrations of hydroxyacetonitrile, etc. In this system, the optimal effect of the acidic catalyst is that it can cooperate with the alkaline solution of sodium or potassium salt and the alanine raw material to form a buffer environment for the catalyst, which is conducive to the stability of the pH during the reaction process and also helps to avoid the effects of imbalances such as excessively high concentrations of added materials and excessively rapid temperature increases, thereby controlling the occurrence of undesirable side reactions.

[0060] In the reaction environment described in the present application, the reaction temperature of the pre-mixed reaction solution with hydrocyanic acid is preferably controlled to be 25-50°C, preferably the reaction temperature in a non-catalyst environment is 25-35°C, and preferably the reaction temperature in an acidic catalyst environment is 35-45°C. It can be seen that in an alkaline environment, in order to control the content of hydroxyacetonitrile in methylglycine-N,N-diacetonitrile and the color number, the reaction temperature needs to be lower. In an environment exceeding 40°C, the possibility of the polymerization and decomposition of hydroxyacetonitrile and its by-products increases, and the Hazen color number of the product increases to some extent with the increase and prolongation of time and temperature. However, in an acidic catalyst environment at 25-50°C, the stability of methylglycine-N,N-diacetonitrile is higher, and the reaction control has a larger flexibility, and the effects of excessively fast addition of hydrocyanic acid to the system or local temperature increases during the reaction will be significantly reduced.

[0061] The acid catalyst can be added in advance in a single batch reaction process, or in liquid or solid form, dissolved in the pre-mixed reaction solution. In a continuous reaction process, such as a tower reaction process, the acid catalyst can be prepared separately into a solution and continuously added, or mixed with a basic solution to form a buffer system and continuously added. Preferably, the concentration of the acid catalyst is 0.1-1.0% by weight, and the amount of catalyst added is 0.5-2.0% of the molar amount of propionic acid.

[0062] In the reaction environment described in the present application, the reaction time of the pre-mixed reaction solution with hydrocyanic acid is preferably 2-6h. During or after the reaction, the pH is optionally adjusted to 2.0-4.5 by adding acid or base, and the optimal pH for the storage of methyl glycine-N,N-diacetonitrile mixture is 3.0-4.2 in a weakly acidic environment.

[0063] The acid used to adjust the pH value of the system described in the present application is preferably an organic acid such as lactic acid, citric acid, acetic acid, or an inorganic acid such as sulfuric acid, phosphoric acid. The base is preferably sodium hydroxide or potassium hydroxide. At the end of the reaction, the final pH value is adjusted while detecting the indicators of the mixture.

[0064] The storage stability of the methyl glycine-N,N-diacetonitrile mixture prepared by the method of the present application is proven to be advantageous, and subsequent specific storage conditions and data can verify its effectiveness through analysis methods and analysis data. As a raw material intermediate, it is further hydrolyzed with sodium hydroxide or potassium hydroxide or potassium carbonate and applied to the preparation of methyl glycine-N,N-diacetic acid and methyl glycine-N,N-diacetic acid trisodium or tripotassium salt. Then, it is applied to the preparation of methyl glycine-N,N-diacetic acid through means such as acid neutralization and crystallization separation.

[0065] Overall, the conversion rate of hydrocyanic acid raw material in the preparation process of methyl glycine-N,N-diacetonitrile mixture reaches 99%, and the conversion rates of formaldehyde and propionic acid raw materials are >99%. Under the same process conditions, the total yield of methyl glycine-N,N-diacetic acid trisodium or tripotassium salt prepared by the existing process is >95%. Subsequent analysis of the MGDA or MGDA·3Na or MGDA·3K content of 30-40% by weight solution product shows that the total NTA content of the product is 0.01-0.1%, the Hazen color number is 30-330, and the content of formaldehyde and formaldehyde release is 5-50ppm.

[0066] The following examples will further illustrate the mixture and its preparation and application provided by the present application, but the present application is not limited to the listed examples, and any other known changes within the scope of the claims of the present application are also included.

[0067] The analysis methods used are described in further detail as follows:

[0068] Water content in methylglycine-N,N-diacetic acid mixture: The water content in the inventive mixture is determined by Karl-Fischer method known to the person skilled in the art by titration using the end-point indication of the double amperometric indication. For this purpose, 30-60 ml of titration medium, for example Hydranal Solvent 5, Fluka or other equivalent titration medium, is first charged into the titration vessel and titrated to dryness with the titrant. A sample quantity of 200-500 mg is added to the titration-dry flask using a disposable plastic syringe and titrated to the end-point with the titrant. The exact sample weight is determined gravimetrically.

[0069] Free cyanide content in methylglycine-N,N-diacetic acid mixture: Determined by silver nitrate potentiometric titration or by ion chromatography IC principle known to the person skilled in the art using an amperometric cyanide detection at a silver electrode with cyanide external standard for quantification.

[0070] Methanol and hydroxyacetonitrile content in methylglycine-N,N-diacetic acid mixture: Determined by gas chromatography, instrument type Agilent 7890B, hydrogen flame ionization detector (FID), recommended chromatographic column capillary column, type HP-VOC, stationary phase 6% -cyanopropyl-phenyl-polymethylsiloxane, column inner diameter 0.32 mm, column length 60 m, carrier gas N2: 1.5 mL / min, column temperature initial temperature 50 °C for 2 min, then temperature increase of 5 °C / min to 80 °C, then temperature increase of 15 °C / min to 250 °C for 10 min, vaporizer chamber temperature 150 °C, detector temperature 260 °C, injection volume 1 μL, split ratio 10:1, hydrogen flow rate 30 mL / min, air flow rate 400 mL / min, tail gas flow rate 25 mL / min. The methanol content is established by gas-phase external standard method by establishing a standard curve for the methanol content, the samples are pre-diluted 5-50-fold with acetonitrile solution according to the concentration range, the hydroxyacetonitrile determination can be carried out using technical-grade 40% or 50% hydroxyacetonitrile, the samples establish a standard curve in the range of 100-1000 mg / kg, likewise the methylglycine-N,N-diacetic acid sample is pre-diluted 5-50-fold with acetonitrile solution according to the content.

[0071] Methylglycine-N,N-diacetic acid mixture content: Determined by ion exclusion chromatography known to the person skilled in the art on a cation exchange column, detection wavelength 205 nm or by high-performance liquid chromatography.

[0072] Methylglycine-N,N-diacetic acid mixture and MGDA product Hazen color number: Liquid chemical product color determination method (platinum-cobalt color number) known to the person skilled in the art.

[0073] Total sodium or total potassium content determination: flame emission spectrometry (refer to GB 5009.91-2017).

[0074] MGDA or MGDA-3Na (3K) content determination method: ferric chloride complex potential titration.

[0075] NTA or NTA-3Na (3K) content: ion chromatography or liquid chromatography quantitative analysis known to those skilled in the art.

[0076] Formaldehyde content in MGDA: acetylacetone spectrophotometry and liquid chromatography (refer to GB / T 35755-2017 Determination of formaldehyde content in surfactants and detergents)

[0077] Example 1 Preparation of methyl glycine-N, N-diethanide mixture (D, L-α-alanine and high-purity hydrocyanic acid, without catalyst)

[0078] 90.3 g of D, L-α-alanine (main content 98.5%, 1 mol, sourced from Balingwei) was added to a four-necked flask with a reflux condenser, and 466.3 g of water was added to partially dissolve it, with the temperature controlled at 25-35°C, and the solution was stirred and cooled. Then 36.7 g (0.2 mol) of 30% potassium hydroxide solution was slowly added dropwise, and after dissolution, a clear solution was obtained, with the initial concentration of alanine being 15% and the pH being 9.0 (20°C). The temperature was controlled at 25-35°C, and 163.8 g (2.020 mol, sourced from Komiyu, containing 2.6% methanol) of 37.0% formaldehyde solution was added dropwise over a period of 1 h, to obtain a total of 757.0 g of pre-mixed reaction solution.

[0079] The solution was stirred at a constant speed, and the temperature was controlled at 25-35°C. Then 55.5 g of industrial-grade hydrocyanic acid (main content 99.2%, 2.039 mol) was slowly added dropwise into the pre-mixed reaction solution, and the speed and temperature were controlled. The total dropwise addition time was 1 h, and after the dropwise addition was completed, the solution was incubated for 1 h. At this time, a sample was taken for analysis (free cyanide 0.18%, pH = 3.6, hydroxyacetonitrile 0.27%), and the reaction was stopped after incubation at 30°C for 2 h. The total weight of the methyl glycine-N, N-diethanide mixture was 812.2 g, which was transferred to a low-temperature sealed container for storage. The detailed analysis indicators were as follows: pH = 3.5, Hazen color number 172, free cyanide 0.13%, hydroxyacetonitrile 0.25%, moisture 77.8%, methyl glycine-N, N-diethanide 20.4%, methanol 0.52%, and total potassium 0.95%.

[0080] Example 2 Preparation of methyl glycine-N, N-diethanide mixture (L-α-alanine and high-purity hydrocyanic acid, without catalyst)

[0081] 89.8 g of industrial grade L-α-alanine (main content 99.1%, 1 mol, from Huaheng Bio) was added to a four-necked flask with a reflux condenser, and 206 g of water was added to partially dissolve it. The temperature was controlled at 25-35°C, and the stirring was cooled. 60 g (0.75 mol) of 50% sodium hydroxide solution was slowly added dropwise. After dissolution, a clear solution was obtained. The initial concentration of alanine was 25%, and the pH was 10.4 (20°C). The temperature was controlled at 25-35°C, and 163 g (2.010 mol, from Comie, containing 2.6% methanol) of 37.0% formaldehyde solution was added dropwise over 1 h. A total of 518.7 g of pre-mixed reaction solution was obtained.

[0082] The stirring speed was controlled at 25-35°C, and 55.5 g of industrial grade hydrocyanic acid (main content 99.2%, 2.039 mol) was slowly added dropwise into the pre-mixed reaction solution. The total dropwise addition time was 1 h, and the temperature was controlled. After the addition was completed, the sample was analyzed (free cyanide 0.15%, pH = 4.3, hydroxyacetonitrile 0.34%) at 30°C for 1 h. The reaction was stopped after 2 h at 30°C. The total weight of the methylglycine-N,N-diacetonitrile mixture was 573.9 g, which was transferred to a low-temperature sealed container for storage. The detailed analysis indicators were as follows: pH = 4.2, Hazen color number 280, free cyanide 0.12%, hydroxyacetonitrile 0.30%, moisture 65.7%, methylglycine-N,N-diacetonitrile 29.1%, methanol 0.75%, and total sodium 3.02%.

[0083] Example 3 Preparation of methylglycine-N,N-diacetonitrile mixture (D,L-α-alanine and high-purity hydrocyanic acid, acidic catalyst)

[0084] 90.3 g of D,L-α-alanine (main content 98.5%, 1 mol, from Bailingwei) was added to a four-necked flask with a reflux condenser, and 590.8 g of water was added to dissolve it. The temperature was controlled at 25-35°C, and the stirring was cooled. 4 g (0.05 mol) of 50% sodium hydroxide solution was slowly added dropwise. After dissolution, a clear solution was obtained. The initial concentration of alanine was 13%, and the pH was 6.7 (20°C). The temperature was controlled at 25-35°C, and 163 g (2.010 mol, from Comie, containing 2.6% methanol) of 37.0% formaldehyde solution was added dropwise over 1 h. A total of 848.1 g of pre-mixed reaction solution was obtained.

[0085] Pre-mixed reaction liquid was added with 3.9 g of solid citric acid (0.02 mol), and 55.5 g of industrial-grade hydrocyanic acid (main content 99.2%, 2.039 mol) was slowly added into the pre-mixed reaction liquid at a temperature of 35-45°C, with the total dropwise adding time being 1.5 h. After the dropwise adding was completed, the reaction was stopped after 1.5 h of incubation, and the sample was analyzed (free cyanide 0.12%, pH=3.1, hydroxyacetonitrile 0.22%). After 2.5 h of incubation at 40°C, the reaction was stopped, and the methyl glycine-N,N-diacetonitrile mixture was weighed to be 907.2 g, which was transferred and stored at low temperature in a sealed manner. Detailed analysis indexes were as follows (pH=3.0, Hazen color number 125, free cyanide 0.10%, hydroxyacetonitrile 0.22%, water content 80.5%, methyl glycine-N,N-diacetonitrile 18.3%, methanol 0.47%, total sodium 0.13%).

[0086] Example 4 Preparation of methyl glycine-N,N-diacetonitrile mixture (D,L-α-alanine, L-α-alanine and high-purity hydrocyanic acid, without catalyst)

[0087] 62.9 g of industrial-grade L-α-alanine (main content 99.1%, 0.7 mol, from Huaheng Bio) and 27.1 g of solid D,L-α-alanine (main content 98.5%, 0.3 mol, from Bailingwei) were added into a four-necked flask with a reflux condenser, and 304 g of water was added to partially dissolve the mixture. The temperature was controlled at 25-35°C, and 52 g of 50% sodium hydroxide solution (0.65 mol) was slowly added dropwise under stirring. After dissolution, the initial concentration of the alanyl was 20%, and the pH was 9.9 (20°C). The temperature was controlled at 25-35°C, and 163 g of 37.0% formaldehyde solution (2.010 mol, from Kemiyou, containing 2.6% of methanol) was slowly added dropwise for 1 h to obtain a pre-mixed reaction liquid with a total weight of 608.8 g.

[0088] The temperature was controlled at 25-35°C, and 55.5 g of industrial-grade hydrocyanic acid (main content 99.2%, 2.039 mol) was slowly added into the pre-mixed reaction liquid, with the total dropwise adding time being 1 h. After the dropwise adding was completed, the sample was analyzed (free cyanide 0.26%, pH=4.1, hydroxyacetonitrile 0.35%) after 1 h of incubation. The reaction was stopped after 2 h of incubation at 30°C, and the methyl glycine-N,N-diacetonitrile mixture was weighed to be 663.9 g, which was transferred and stored at low temperature in a sealed manner. Detailed analysis indexes were as follows (pH=4.0, Hazen color number 255, free cyanide 0.14%, hydroxyacetonitrile 0.29%, water content 70.8%, methyl glycine-N,N-diacetonitrile 25.1%, methanol 0.65%, total sodium 2.25%).

[0089] Example 5 Preparation of methylglycine-N,N-diacetic acid mixture (D,L-α-alanine, L-α-alanine and high purity hydrocyanic acid, acidic catalyst)

[0090] 18.0 g of industrial grade L-α-alanine (main content 99.1%, 0.2 mol, from Huaheng Bio) and 72.3 g of solid D,L-α-alanine (main content 98.5%, 0.8 mol, from Bailingwei) were added to a four-necked flask with a reflux condenser, dissolved in 1014 g of water, the temperature was controlled at 25-35°C, and the solution was stirred and cooled. 8 g of 50% sodium hydroxide solution (0.10 mol) was slowly added dropwise. After dissolution, a clear solution was obtained, the initial concentration of alanine was 8%, and the pH was 7.5 (20°C). The temperature was controlled at 25-35°C, and 163 g of 37.0% formaldehyde solution (2.010 mol, from Kaimiyou, containing 2.6% methanol) was added dropwise over 1 h. A total of 1275.0 g of pre-mixed reaction solution was obtained.

[0091] 2.7 g of malic acid (0.02 mol) was added to the pre-mixed reaction solution, the temperature was controlled at 35-45°C, and 55.5 g of industrial grade hydrocyanic acid (main content 99.2%, 2.039 mol) was slowly added dropwise into the pre-mixed reaction solution. The total dropwise addition time was 1.5 h, and the temperature and speed were controlled. After the dropwise addition was completed, the solution was incubated for 1.5 h, and samples were taken for analysis (free cyanide 0.11%, pH=3.3, hydroxyacetonitrile 0.12%) at this time. The reaction was stopped after incubation at 40°C for 2.5 h. A total of 1333.0 g of methylglycine-N,N-diacetic acid mixture was weighed and stored in a transfer cryogenic sealed container. The detailed analysis indicators were as follows: pH=3.3, Hazen color number 135, free cyanide 0.10%, hydroxyacetonitrile 0.11%, moisture 86.7%, methylglycine-N,N-diacetonitrile 12.5%, methanol 0.31%, and total sodium 0.17%.

[0092] Comparative Example 1 (same as Example 2) Preparation of methylglycine-N,N-diacetic acid mixture (L-α-alanine and high purity hydrocyanic acid, no catalyst)

[0093] 89.8 g of industrial grade L-α-alanine (main content 99.1%, 1 mol, from Huaheng Bio) was added to a four-necked flask with a reflux condenser, and 186 g of water was added to partially dissolve it. The temperature was controlled at 25-35°C, and the solution was stirred and cooled. 80 g of 50% sodium hydroxide solution (1.0 mol) was slowly added dropwise. After dissolution, a clear solution was obtained, the initial concentration of alanine was 25%, and the pH was 13.5 (20°C). The temperature was controlled at 25-35°C, and 163 g of 37.0% formaldehyde solution (2.010 mol, from Kaimiyou, containing 2.6% methanol) was added dropwise over 1 h. A total of 518.5 g of pre-mixed reaction solution was obtained.

[0094] The temperature was controlled at 25-35°C, and 55.5 g of industrial-grade hydrocyanic acid (main content 99.2%, 2.039 mol) was slowly added into the pre-mixed reaction solution. The total dropwise addition time was 1 h. After the dropwise addition was completed, the sample was analyzed (free cyanide 1.13%, pH = 7.8, hydroxyacetonitrile 0.85%) when the temperature was controlled at 30°C for 1 h. The reaction was stopped after the temperature was controlled at 30°C for 2 h. The total amount of the methyl glycine-N,N-diacetonitrile mixture was 573.5 g, which was transferred and stored at low temperature in a sealed manner. The detailed analysis indexes were as follows (pH = 7.9, Hazen color number 850, free cyanide 1.07%, hydroxyacetonitrile 1.65%, water content 65.3%, methyl glycine-N,N-diacetonitrile 18.9%, methanol 0.73%, and total sodium 4.0%).

[0095] Comparative Example 2 (same as Comparative Example 3) Preparation of a methyl glycine-N,N-diacetonitrile mixture (D,L-α-alanine and high-purity hydrocyanic acid, acidic catalyst)

[0096] 90.3 g of D,L-α-alanine (main content 98.5%, 1 mol, from Balingwei) was added into a four-necked flask with a reflux condenser, and 594.3 g of water was added for dissolution. The temperature was controlled at 25-35°C. The initial concentration of the alanine was 13%, and the pH was 6.0 (20°C). 163 g (2.010 mol, from Komiyu, containing 2.6% of methanol) of a 37.0% formaldehyde solution was added dropwise. The dropwise addition time was 1 h. The total amount of the pre-mixed reaction solution was 847.5 g.

[0097] 3.9 g (0.02 mol) of citric acid was added into the pre-mixed reaction solution, and the temperature was controlled at 35-45°C. 55.5 g of industrial-grade hydrocyanic acid (main content 99.2%, 2.039 mol) was slowly added into the pre-mixed reaction solution. The total dropwise addition time was 1.5 h. After the dropwise addition was completed, the sample was analyzed (free cyanide 0.23%, pH = 1.3, hydroxyacetonitrile 0.12%) when the temperature was controlled at 40°C for 1.5 h. The reaction was stopped after the temperature was controlled at 40°C for 2.5 h. The total amount of the methyl glycine-N,N-diacetonitrile mixture was 906.7 g, which was transferred and stored at low temperature in a sealed manner. The detailed analysis indexes were as follows (pH = 1.1, Hazen color number 125, free cyanide 0.20%, hydroxyacetonitrile 0.13%, water content 80.7%, methyl glycine-N,N-diacetonitrile 17.5%, and methanol 0.46%).

[0098] According to Examples 1-5 and Comparative Examples 1-2, the methyl glycine-N,N-diacetonitrile mixture was obtained. The stability was verified through storage experiments under the same storage temperature environment (8°C). The parameters were determined under the same analysis conditions (20°C).

[0099] Table 1 Dependence of the content of the methyl glycine-N,N-diacetonitrile mixture on the storage time and color number

[0100]

[0101] From Table 1, it can be seen that the products prepared in Examples 1-5, with the increase of time, the pH of methyl glycine-N,N-diacetonitrile mixture is 3.0-4.2, the content decreases by 0.19%-0.25% at most for 120 days, and the color number increases by no more than 20; the initial pH of Comparative Example 1 is 7.9, the basic environment and high content of cyanide and hydroxyacetonitrile in the product are not conducive to the stability of the product, the color number of the product rises, and the product is decomposed and polymerized in less than 3 days of storage; in Comparative Example 2, the initial pH is 1.1, the acidic environment is conducive to the stability of the color number, but the residual unreacted cyanide and hydroxyacetonitrile, and the too strong acidity can cause the decomposition of nitriles, the content of the product decreases by 1.2% at most for 30 days and by 1.6% at most for 120 days, affecting the yield of the product.

[0102] Example 6 further verifies the stability of the product prepared in the application by controlling the content of hydrocyanic acid and hydroxyacetonitrile at the end of the reaction, adjusting the content of hydrocyanic acid and hydroxyacetonitrile by external addition, adjusting the pH value of the system by acid and alkali, and storing at 8°C and 18°C for 120 days.

[0103] Table 2 Relationship between content of methyl glycine-N,N-diacetonitrile, color number, pH value, free cyanide and hydroxyacetonitrile

[0104]

[0105]

[0106] From Table 2, it can be seen that the product prepared in Example 2, in a storage environment of 8°C and 18°C, the content of methyl glycine-N,N-diacetonitrile mixture decreases by 0.19%-0.32% at most for 120 days, and the color number increases by no more than 32; after adding hydrocyanic acid and hydroxyacetonitrile in Comparative Example 3, the content of cyanide and hydroxyacetonitrile in the product is >0.5%, the color number increases by 100 at most for 120 days, and the content decreases by 0.65%; in Comparative Example 4, the product stability decreases by adjusting the pH value to 6 by alkali, the content decreases by 0.55% at most for 30 days and by 1.9% at most for 120 days, affecting the yield of the product, and the color number increases significantly. The content of hydrocyanic acid and hydroxyacetonitrile and the pH value of the system are the key factors affecting the stability of methyl glycine-N,N-diacetonitrile mixture.

[0107] Example 7 The methyl glycine-N, N-diethylnitrile mixture is applied to prepare methyl glycine diacetic acid trisodium salt product, referring to the same preparation process of MGDA.3Na solution in CN103476741B, the methyl glycine-N, N-diethylnitrile mixture is slowly added into 50% sodium hydroxide solution 189g (2.36mol), the reaction is carried out at 40-50℃, the dropping is carried out for 1h, the temperature is kept for 1h, then the temperature is raised to 95-102℃, the hydrolysis is carried out for 4h, ammonia is discharged and concentrated by evaporation to the content of 40% MGDA.3Na. The methyl glycine-N, N-diethylnitrile mixture prepared by different storage time in example 2 and the methyl glycine-N, N-diethylnitrile mixture prepared in comparative examples 3 and 4 are applied to prepare 40% MGDA.3Na solution by hydrolysis, the comparison data are shown in table 3.

[0108] Table 3 Data comparison of methyl glycine-N, N-diethylnitrile mixture applied to prepare 40% MGDA.3Na solution

[0109]

[0110] It can be seen that the product prepared in example 2 of the present application, the content of methyl glycine-N, N-diethylnitrile mixture is reduced by 0.19%-0.32% at most for 120 days in 8℃ and 18℃ storage environment, the overall yield of the downstream product MGDA.3Na prepared by the same process is 96.65%-97.05%, which is consistent with the product yield of the prior art, at the same time, through the comparative examples, the product yield, color number and by-product NTA all remain the optimal level.

[0111] Although the content of the present application has been described in detail by the above preferred examples, it should be recognized that the above description should not be considered as a limitation of the present application. Those skilled in the art can understand that some modifications or adjustments can be made to the present application under the teaching of the present specification. These modifications or adjustments should also be within the scope defined by the claims of the present application.

Claims

1. A storage-stable methylglycine-N,N- diacetic acid composition characterized in that, 5.0-40.0% methylglycine-N,N-diacetic acid, 0.1-5.0% sodium or potassium ion, 0.1-1.5% methanol or ethanol, 0.05-0.5% hydrocyanic acid, 0.05-0.5% hydroxyacetonitrile, the rest being water; and the composition has a pH of 2.0-4.5 and a Hazen color number of 10-350 under test conditions at 20°C.

2. A storage-stable methylglycine-N,N- diacetic acid composition according to claim 1, wherein, 8.0-35.0% methylglycine-N,N-diacetic acid, 0.1-3.5% sodium or potassium ion, 0.1-0.9% methanol or ethanol, 0.1-0.3% hydrocyanic acid, 0.1-0.3% hydroxyacetonitrile, the rest being water; and the composition has a pH of 3.0-4.2 and a Hazen color number of 20-280 under test conditions at 20°C.

3. Process for the preparation of the storage-stable methylglycine-N,N- diacetonitrile composition according to claim 1 or 2, characterized in that The method comprises the following steps: a) adding a formaldehyde solution to a mixed solution of α-alanine and an alkali metal salt of α-alanine to prepare a premixed reaction solution; b) reacting the premixed reaction solution with hydrocyanic acid in the presence of an acidic catalyst or without a catalyst to prepare methylglycine-N,N-diacetic acid, and during or after the reaction, the content of hydrocyanic acid is controlled to be 0.05-0.5% by weight by adding hydrocyanic acid, and the content of hydroxyacetonitrile is controlled to be 0.05-0.5% by weight by adding hydrocyanic acid; c) during or after the reaction, the pH is adjusted to be 2.0-4.5 by adding an acid or a base.

4. The production method according to claim 3, characterized by, In step b), the content of hydrocyanic acid is controlled to be 0.1-0.3% by weight by adding hydrocyanic acid, and the content of hydroxyacetonitrile is controlled to be 0.1-0.3% by weight by adding hydrocyanic acid; In step c), the pH is adjusted to be 3.0-4.2 by adding an acid or a base.

5. The preparation method according to claim 3, characterized in that, The molar ratio of α-alanine:hydrocyanic acid:formaldehyde is 1.0:(2.02-2.06):(2.01-2.05).

6. The preparation method according to claim 3, characterized in that, The acidic catalyst in step b) is selected from one or more of lactic acid, citric acid, tartaric acid, malic acid, ascorbic acid, acetic acid, succinic acid, and oxalic acid.

7. The preparation method according to claim 3, characterized in that, The acid in step c) is an organic acid or an inorganic acid.

8. The preparation method according to claim 7, characterized in that, The organic acid is selected from any one of lactic acid, citric acid, and acetic acid, and the inorganic acid is selected from sulfuric acid or phosphoric acid.

9. The preparation method according to claim 3, characterized in that, The hydrocyanic acid is obtained from synthesis gas by methanol ammonia oxidation or methane ammonia oxidation, and the obtained hydrocyanic acid mixture has a content of 5-15% by weight, or the refined liquid hydrocyanic acid obtained by any process has a content of >99% by weight.

10. Use of the composition of claim 1 or 2 or the storage-stable methylglycine-N,N-diacetic acid composition prepared by the method of any one of claims 3-9 for storing methylglycine-N,N-diacetic acid.

11. Use according to claim 10, characterized in that, The storage time is at least 1 month at a storage temperature of 0°C-50°C.

12. Use according to claim 11, characterized in that, The storage time is up to 6 months at a storage temperature of 5°C-25°C.

13. Use according to claim 12, characterized in that, The storage time is up to 4 months at a storage temperature of 5°C-18°C.

14. Use of a storage-stable methylglycine-N,N-diacetic acid tri-sodium salt and / or a storage-stable methylglycine-N,N-diacetic acid tri-potassium salt prepared from the composition of claim 1 or 2 or prepared by the method of any one of claims 3 to 9.

15. Use of a storage-stable methylglycine-N,N-diacetic acid prepared from the composition of claim 1 or 2 or prepared by the method of any one of claims 3 to 9.

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