CN1478784A - New technology for preparating N-phosphono methyl glycine - Google Patents

Abstract

A process for synthesizing the glyphosate from the alkali metal salt of glycine includes such steps as acidifying with inorganic acid to obtain glycine and inorganic salt, concentrating, drying to obtain the mixture of glycine and salt, adding formaldehyde, alkyl phosphite, tetraamine as catalyst and unitary alcohol as solvent, and reaction to synthesize glyphosate as herbicide while separate out inorganic salt insoluble in the system.

Description

New process for preparing N-phosphono methyl glycine

One, the technical field

The invention relates to a preparation method of herbicide N-phosphono methyl glycine (glyphosate) by taking alkyl phosphite as a main raw material.

Second, background Art

The glyphosate acid is known by the chemical name of N-phosphonomethylglycine (PMG for short), and has the molecular formula:the glyphosate-tolerant herbicide is an efficient broad-spectrum biocidal herbicide, has good systemic conductivity, is very effective in preventing and controlling various deep-rooted malignant weeds, has gradually increased sales volume in recent years, further expands the application range along with the gradual popularization of glyphosate-tolerant transgenic crops, becomes a herbicide with the largest sales volume and the fastest growth speed in the world, and has the global sales volume of glyphosate reaching $ 30 hundred million in 2002 and accounting for 10 percent of the total sales volume of pesticides.

Two main industrial glyphosate acid production processes exist, one is an IDA route which is adopted by Monsanto USA and takes hydrocyanic acid or diethanolamine as a starting material; the other is a dialkyl phosphite route which is generally adopted in China and takes glycine as a starting material. Both processes can obtain glyphosate acid raw powder with the content of not less than 93.5 percent.

To date, numerous studies have been developed around the IDA route, such as US5312973, US5023369 which disclose a process for preparing pmida due to iminodiacetic acid (IDA) and glyphosate acid from pmida oxidation, respectively; ZL93120707 and ZL96195765 also disclose a method for synthesizing N- (phosphonomethyl) iminodiacetic acid from alkali metal iminodiacetate and preparing glyphosate acid by oxidizing N- (phosphonomethyl) iminodiacetic acid with hydrogen peroxide respectively.

The research on the dialkyl phosphite route is very little, and the invention patent with the application number of 85102988 discloses a preparation process of glyphosate by taking dialkyl phosphite as a raw material; the invention patent with application number 00125933 discloses an improvement of glyphosate by dialkyl acid method of phosphorous acid, which uses byproduct methylal of itself to synthesize glyphosate instead of paraformaldehyde, and the research on glyphosate synthesis process by trimethyl phosphite (PESTICIDES, 1999.Vol.38 NO. 6P 8) introduces a method for synthesizing PMG in aqueous phase by trialkyl phosphite and glycine.

However, the production of glyphosate acid in China is different from that in foreign countries, due to the factors of raw materials, the dialkyl phosphite route is well developed, the production scale of the dialkyl phosphite route is nearly 8 ten thousand tons/year, and the dialkyl phosphite route has more advantages compared with the IDA route in terms of product quality:

the prior art of dialkyl phosphate route requires high quality of glycine as main raw material, and "production and development trend of glycine" ("Chinese petroleum and chemical analysis report" 2002, 6 th page 13) discloses that the quality of glyphosate acid is affected by the existing glycine production process (chloroacetic acid ammonolysis method) due to low product quality. The problem is now that the purification cost of glycine is very high: the chloroacetic acid ammonolysis method needs a large amount of alcohol to separate glycine and ammonium chloride as byproducts, and the recovery of the alcohol needs a large amount of energy consumption, so that the cost is increased; the difficulty of obtaining high-purity glycine from glycine alkali metal salt obtained by monoethanolamine catalytic dehydrogenation and hydrocyanic acid method is higher, and the electrodialysis process disclosed by the novel glycine process by an ion membrane method (Henan chemical engineering 2001.1P19) is limited by membranes, so that the working concentration is lower, and the refining cost of the glycine is higher due to the fact that the glycine has 4-9% of escape rate. Therefore, although monoethanolamine and hydrocyanic acid can be obtained as by-products, and thus the raw material cost is low, the purification cost is too high, and the purification method has not been industrialized so far in China.

Therefore, the problem that the prior art does not solve is that the product quality of the dialkyl phosphate method glyphosate is good but the cost of the main raw material glycine is high.

The invention aims to solve the problems and improve the prior dialkyl phosphate method glyphosate process, so as to obtain glyphosate acid at relatively lower cost.

Third, the invention

The invention provides a method for synthesizing glyphosate acid by taking alkali metal glycinate as a raw material, which comprises the steps of acidifying the alkali metal glycinate by using inorganic acid to obtain glycine and inorganic salt, then concentrating and drying to obtain a mixture of the glycine and the salt (hereinafter referred to as mixed crystal), synthesizing the glyphosate acid by using the mixed crystal, formaldehyde and alkyl phosphite by using tertiary amine as a catalyst and using monohydric alcohol with the carbon atom number of 1-4 as a solvent, and separating out inorganic salt which is insoluble in a system in the process.

The tertiary amine is preferably triethylamine.

The monohydric alcohol is preferably methanol.

The inorganic salt has solubility in methanol of less than 2g, and can be sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, and potassium nitrate.

The inorganic acid is characterized in that the solubility of the sodium salt or the potassium salt thereof in methanol is less than 2g, such as hydrochloric acid, sulfuric acid and nitric acid.

The weight content of the glycine in the mixed crystal is 20-95%.

The glycine alkali metal salt is sodium glycinate or potassium glycinate and can be obtained by a plurality of methods, and the invention comprises the glycine alkali metal salt obtained by the following two schemes of ① catalytic dehydrogenation of monoethanolamine in liquid alkali to obtain an aqueous solution of sodium aminoacetate:

② the cyanamide is prepared from hydrocyanic acid (sodium hydride) and is subjected to alkaline hydrolysis by the cyanamide:

in the above scheme, potassium glycinate is obtained if potassium hydroxide is used, and sodium glycinate or potassium glycinate is acidified by inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid to obtain mixed aqueous solution of glycine and inorganic salts (sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate and potassium nitrate). Since the salts have similar solubility characteristics to those of glycine in water and organic solvents, it is difficult to obtain highly pure glycine by simple purification, which has been conventionally performed by desalting by electrodialysis or ion exchange, and then concentrating to obtain glycine crystals. The invention breaks through the traditional concept that glyphosate has to be high-purity glycine in alkyl phosphite process, finds the key step that the low-content glycine influences the quality of glyphosate, and combines the separation of glycine and inorganic salt with the production process of glyphosate, so as to obtain the inorganic salt with higher purity while producing the glyphosate raw powder by a very simple method. Because the purification step of the glycine is saved, the loss of the glycine is reduced, the discharge amount of three wastes in the production process is reduced, and high-content byproduct inorganic salt can be obtained, which can be obtained by one stroke, thereby greatly reducing the cost for producing the herbicide glyphosate acid. The invention reduces the water content in the mixed water solution of the glycine and the inorganic salt to obtain the mixed crystal of the glycine and the inorganic salt, and the adopted method can be simple evaporation, reduced pressure evaporation, multi-effect evaporation and direct spray drying; or by adding C1-4 monohydric alcohol (preferably methanol) into the mixed aqueous solution to reduce the solubility of glycine and inorganic salt in the system, crystallizing, and filtering. Before being used for preparing glyphosate acid, the obtained mixed crystal is dried and the moisture content in the mixed crystal is controlled to be less than 3 percent.

The prior art for synthesizing glyphosate acid by using glycine as a raw material comprises the steps of adding paraformaldehyde into methanol, adding triethylamine, heating to depolymerize the paraformaldehyde, adding glycine for addition reaction, adding dimethyl phosphite or trimethyl phosphite for condensation reaction after clarification, adding hydrochloric acid for hydrolysis, dealcoholizing and filtering to obtain the glyphosate acid. If the content of the raw material impurities is too high, part of the impurities are finally mixed in the glyphosate acid, and the quality of the glyphosate acid is influenced. Since most inorganic salts have very low solubility in alcohol, for example, KCl has a saturation concentration of 0.417% in methanol at 20 ℃, NaCl has a saturation concentration of 1.39% in methanol at 19.5 ℃, and NaNO₃The saturated concentration in methanol at 19.5 ℃ was 0.41%, Na₂SO₄At 20The saturation concentration of the glyphosate in methanol at the temperature of 0.25 percent is inert in a glyphosate reaction system, so that the inorganic salt which is not dissolved in the system can be filtered and taken out after the addition reaction or the condensation reaction is finishedIn addition, one or a combination of several separation methods such as sedimentation, suction filtration, filter pressing, centrifugation and the like can be adopted for separation. Because the inorganic salt dissolved in the system is very little, the quality of the glyphosate acid product is not affected. By adopting the scheme, the recovery rate of the inorganic salt can reach 95-99.5%, the total yield (calculated by glycine) of the glyphosate acid can reach 82-88%, and compared with the preparation of the glyphosate acid by adopting high-purity glycine, the method has no influence.

The technical scheme provided by the invention makes it possible to synthesize glyphosate by adopting low-content glycine, and can separate out byproduct inorganic salt in the reaction process by a very simple method, thereby reducing the production cost.

Fourth, detailed description of the invention

The invention is described below in terms of specific processes,the contents being used in weight percent.

Example 1-1 1000g of a 34% strength aqueous solution of sodium glycinate was taken, 215g of 80% strength sulfuric acid was added, the mixture was stirred well, the pH was measured to be 6, the mixture was concentrated by heating under a vacuum of 0.08MPa, and 598g of water was distilled off. Cooling to 25 ℃, filtering and drying to obtain 458g of mixed crystal of glycine and sodium sulfate, wherein the glycine content is 52 percent, and the sodium sulfate content is 48 percent.

Example 1-2 1000g of a 34% strength aqueous solution of sodium glycinate was taken, 415g of 31% strength hydrochloric acid was added thereto, the mixture was sufficiently stirred, the pH was measured to be 5, the mixture was concentrated by heating under a vacuum of 0.08MPa, and 804.5g of water was distilled off. Then cooling to 25 ℃, filtering and drying to obtain 382.7g of mixed crystal of glycine and sodium chloride, wherein the glycine content is 60.2 percent and the sodium chloride content is 39.8 percent.

Example 2-1 (control example) 120g of methanol, 18g of paraformaldehyde and 35g of triethylamine were taken and placed in a 500ml four-neck flask, the temperature was controlled at 30-50 ℃, 21.5g of glycine with 99.8% content was added after the materials were clarified (referred to as depolymerization), the temperature was controlled at 35-55 ℃, 35g of dimethyl phosphite was added after the materials were clarified (referred to as addition), the temperature was controlled at 40-65 ℃, the reaction was carried out for 50-120min (referred to as condensation), the mixture was cooled to room temperature, 125g of 30% hydrochloric acid was added, the solvent methanol was removed by heating, the mixture was cooled to room temperature, suction filtration was carried out on 196.8g of mother liquor, the glyphosate content was 1.9%, 38.1g of 96.1% glyphosate acid powderwas obtained after drying the filter cake, the solid yield was 75.8%, and the total yield was 83.5%.

Example 3-1 41.3g of the mixed crystal obtained in example 1-1 was taken out and filtered at the end of the addition according to the protocol of example 2-1, the filter cake was washed with 20ml of methanol, the washing solution was incorporated into the filtrate, and the filter cake was dried to give 19.5g, the sodium sulfate content was 99.1%; the yield of sodium sulfate was 97.48%, as in example 2-1.

Example 3-2 41.3g of the mixed crystal obtained in example 1-1 was taken out and filtered at the end of the condensation according to the protocol of example 2-1, the filter cake was washed with 20ml of methanol, the washing solution was incorporated into the filtrate, and the filter cake was dried to give 19.4g with a sodium sulfate content of 98.8%; the yield of sodium sulfate was 96.69%, as in example 2-1.

Example 3-3 35.6g of the mixed crystal obtained in example 1-2 was taken and filtered according to the protocol of example 2-1 at the end of the addition, the filter cake was washed with 20ml of methanol, the washing solution was incorporated into the filtrate, and the filter cake was dried to obtain 12.3g, the sodium chloride content was 99.3%; the yield of NaCl was 86.2%, as in example 2-1.

Example 3-4 35.6g of the mixed crystal obtained in example 1-2 was taken, and the process was carried out according to the protocol of example 2-1, and after the condensation was completed, filtration was carried out, the filter cake was washed with 20ml of methanol, the washing solution was incorporated into the filtrate, and the filter cake was dried to obtain 12.3g, the sodium chloride content was 99%; the yield of sodium chloride was 85.9%, as in example 2-1.

Examples	Weight of raw powder	Content of raw powder	Weight of mother liquor	Content of mother liquor	Yield of solids	Overall yield of
							g	％	g	％	％	％
	3-1	39.2	95.8	183.7	1.8	77.7							84.5
3-2							39.0	95.3	190.4	1.7	76.9	85.9
	3-3	38.3	95.3	189.8	2.0	75.8							83.3
3-4							37.9	95.3	198.7	1.7	74.7	81.7
	2-1 (control)	38.1	96.1	196.8	1.9	75.8							83.5

Claims (12)

1. A process for preparing N-phosphono-methyl glycine from alkali metal glycinate includes acidifying alkali metal glycinate by inorganic acid to obtain glycine and inorganic salt, reducing water content to obtain mixed crystal of glycine and salt, and separating ② inorganic salt insoluble in system.

2. The method according to claim 1, wherein the inorganic salt has a solubility in methanol of less than 2g, and may be selected from the group consisting of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, and potassium nitrate.

3. The method of claim 1, wherein the inorganic acid is selected from the group consisting of a sodium salt, a potassium salt, hydrochloric acid, sulfuric acid, nitric acid, and mixtures thereof, and has a solubility in methanol of less than 2 g.

4. The process according to claim 1, wherein the mixed crystal contains glycine in an amount of 20 to 95% by weight, preferably 40 to 60% by weight.

5. The method of claim 1, wherein said alkali metal salt of glycine is sodium glycinate or potassium glycinate.

6. The process of claim 5, wherein said sodium or potassium glycinate is obtained by catalytic dehydrogenation of monoethanolamine in liquid base.

7. The process of claim 5 wherein said sodium or potassium glycinate is prepared by hydrolysis of aminoacetylcyanide in aqueous sodium or potassium hydroxide.

8. The method of claim 1, wherein the method for obtaining the mixed crystal is concentration, and the method can be atmospheric evaporation, reduced pressure evaporation, multi-effect evaporation and spray drying.

9. The method of claim 1, wherein the method of obtaining mixed crystals comprises adding a monohydric alcohol having 1 to 4 carbon atoms to an aqueous solution of sodium glycinate and an inorganic salt to reduce the solubility of glycine and the inorganic salt in the system and crystallize out. The alcohol used is preferably methanol.

10. The method according to claim 8 or 9, further comprising the step of drying the mixed crystal and controlling the water content therein to less than 3%.

11. The method according to claim 1, wherein the method for separating the inorganic salt insoluble in the system is one or a combination of sedimentation, suction filtration, pressure filtration and centrifugation.

12. The method of claim 1, wherein the inorganic salt is isolated after the addition reaction or after the condensation reaction.