Issue 46, 2013 - Research Progress on Glyphosate Synthesis Process by Iminodiacetic Acid

Research Progress
on Glyphosate Synthesis Process by Iminodiacetic Acid□ Xiaoming
glyphosate is a broad-spectrum biocidal organophosphorus herbicide with good conductivity and has a wide range of uses in agriculture and other aspects
.
At present, the industrial production methods of glyphosate mainly include glycine
method and iminodiacetic acid (IDA).
Among them, the IDA route is currently the most advanced production process, and the glyphosate produced using this route accounts for more than
75% of the total production.
There are two key points of this route: one is the synthesis of the intermediate product IDA, and the other is the oxidation
of bisglyphosate.


At present, the synthesis of IDA is mainly used in the chloroacetic acid method (which has been eliminated), the hydrocyanic acid method, the diethanolamine method and the nitrogen triacetic acid method
.
Among them, the hydrocyanic acid method is currently the main method for synthesizing IDA in the world, using hydrocyanic acid, formaldehyde and methenamine as raw materials to react to prepare iminodiacetonitrile, and then hydrolyzed and acidified to obtain IDA
.
This method is suitable for large-scale production and has high production efficiency, and the purity of IDA can reach 95%.

At present, the foreign raw material hydrocyanic acid comes from the by-product tail gas of the production of acrylonitrile, which has the advantage
of low raw material cost and price.
Due to the lack of a cheap source of hydrocyanic acid in China, this method has not been well promoted
.
At present, Sichuan Research Institute of Chemical Industry and Chongqing Ziguang Chemical Plant have mastered the technology of natural gas to produce hydrocyanic acid and have been put into production
.

The diethanolamine method is to prepare IDA
by catalytic dehydrogenation using diethanolamine and sodium hydroxide as raw materials.
This method is simple and the relevant research is relatively early, in this method using amorphous alloy as a catalyst, while using bipolar membrane electroosmosis technology to synthesize IDA, the conversion rate of diethanolamine is as high as 99%, and the yield of IDA production reaches 95%.

The catalyst can be reused
.
However, due to the lack of raw material diethanolamine source in China, and the cost of imports is high, the large-scale industrial production of this method is limited
.

The nitrogen triacetic acid method reacts with chloroacetic acid and ammonia to obtain nitrogen triacetic acid, and then obtains IDA
by oxidative formaldehyde.
The advantages of this method are low raw material price, simple route, high product yield, and the disadvantage is that the product yield is too sensitive to reaction conditions, so large-scale industrial production
cannot be achieved.

Preparation of glyphosate by oxidation Glyphosate bisglyphosate oxidation preparation of glyphosate
can be divided into chemical oxidation method and catalytic oxidation method
.
Commonly used chemical oxidation methods are concentrated sulfuric acid oxidation, hydrogen peroxide oxidation and electrolytic oxidation
.
Among them, the concentrated sulfuric acid oxidation method has been eliminated
due to the shortcomings of poor product quality and serious pollution.
Hydrogen peroxide oxidation method is the only method to achieve industrial production and is still being applied in China, the method has the characteristics of simple post-treatment and high yield, but this method requires the use of a large amount of hydrogen peroxide, and the oxidation temperature is difficult to control, in addition, the reaction mother liquor contains a large number of metal salts, which not only leads to difficult separation, but also reduces the yield and purity
of glyphosate.
Electrolytic oxidation has not yet been industrialized
due to high energy consumption.

The catalytic oxidation of glyphosate generally uses oxygen or oxygen-containing gas as the oxidant, and glyphosate is synthesized from bisglyphosate under the action of a catalyst, which belongs to the category of green chemistry, and the yield and purity of the product are high
.
The selection, preparation and recycling of efficient catalysts are key
to this process.
The use of activated carbon catalytic oxidation of glyphosate synthesis of glyphosate has the advantages of low cost, high product yield and environmental friendliness, since its development, it has attracted people's attention, and China has achieved industrialization
.
Monsanto and Dow Agro in the United States both use activated carbon supported precious metals as catalysts to catalyze the oxidation of bisglyphosate
by air.
Salts or complexes of common transition metals such as aluminum, iron, manganese, cobalt, lead, chromium, ruthenium, molybdenum, vanadium, silver, tin, etc.
can also be used as catalysts
.
Although the transition metal catalyst is easy to separate glyphosate after reaction, it is difficult to achieve reuse.
At the same time, its catalytic effect is not as good as that of noble metal catalysts, and the conversion rate and product selectivity of bisglyphosate are low
.
In addition, it can also be used to irradiate ultraviolet light source or use activated carbon to co-catalyze the synthesis of glyphosate
by diglyphosate.

Technological progressZhou
Shuguang of East China University of Science and Technology and others synthesized glyphosate by catalytic oxidation using bisglyphosate
and oxygen as raw materials and activated carbon as catalysts.
The results show that the selection of oxygen as raw material reduces the reaction temperature and pressure, and reduces the reaction time to improve the yield
.
The best process conditions were determined: m (catalyst) / m (bisglyphosate) = 0.
188, reaction temperature 45 °C, reaction pressure 0.
5MPa, reaction time 5h
.
Under this condition, the total yield of glyphosate was 97.
1%.


Guo Jianmin of Zhejiang University of Technology et al.
used bisglyphosate as the starting material, oxidized by hydrogen peroxide, catalyzed the synthesis of the herbicide glyphosate, and when synthesizing glyphosate, ferrous sulfate and salt A were used to jointly catalyze the synthesis
of glyphosate.
Under the reaction temperature of 71 °C, the droplet adding time of hydrogen peroxide for 2 h, n (bisglyphosate): n (hydrogen peroxide) = 1:1.
4, the holding time of 12 h, the holding temperature of 64 °C and other optimal process conditions, the total yield of the reaction reached 85.
9% and the content was 94.
0%.


Wang Wei of Zhejiang Xinan Chemical Group Co.
, Ltd.
and others have developed a method
for preparing glyphosate by oxidation of bisglyphosate.
Alkyl hydroanthraquinone or hydroanthraquinone dissolved in organic solvents is added to the bisglyphosate-water system in the presence of catalyst tungstate, and then oxygen-containing gas is introduced into the reaction system for oxidation reaction to obtain a reaction solution; The obtained reaction solution was used as a reactant, and the catalyst ferrous sulfate or sodium sulfite was added for decarboxylation reaction, and the glyphosate was crystallized and purified
.
Glyphosate is prepared by this method, because alkyl hydroanthraquinone or hydroanthraquinone can be recycled in the reaction, and the loss in the process is very small; And because of the use of convenient and readily available air or oxygen as an oxidant and the avoidance of the use of activated carbon catalysts loaded with heavy metals, the by-product hydrogen produced in the preparation of glyphosate can also be utilized, and the utilization rate of raw materials in the whole process is improved, so the cost is
cheaper.
Wang Wei et al.
also developed a method
for producing glyphosate by catalytic oxidation of high-concentration bisglyphosate with oxygen-rich gas.
The method is prepared by adding bisglyphosate and activated carbon to an autoclave for oxidation reaction with high concentration bisglyphosate as raw material, activated carbon as catalyst and oxygen-rich gas as oxidant
.

Wang Wen et al.
of Zhejiang Longyou Lvde Pesticide Chemical Co.
, Ltd.
have developed a method
for catalytic oxidation of resource reuse to prepare glyphosate 。 100 mass bisglyphosate was added to 2~8 mass catalyst, oxygen-containing gas was introduced into the aqueous phase for catalytic oxidation reaction, the reaction temperature was 70~120 °C, and the reaction pressure was 0.
7~1.
2MPa; after the end of the reaction, the catalyst was separated within 1~30 minutes by the solid-liquid separation device, and the reaction liquid was cooled and filtered to separate the solid glyphosate; The filtered mother liquor is separated by the pervaporation membrane separation device to separate the by-product formaldehyde, glyphosate mother liquor is recycled, the separated dilute formaldehyde aqueous solution is separated and concentrated by the pervaporation membrane separation device, and the concentrated formaldehyde is fully or partially recycled
.

Guo Yulai of Beijing Tsinghua Unigroup Yingli Chemical Technology Co.
, Ltd.
and others have developed a new process
for preparing glyphosate by air oxidation of bisglyphosate.
This method directly uses air or oxygen as an oxidant, and can oxidize bisglyphosate to glyphosate
with high yield through the combined catalysis of activated carbon or carbon nanotubes and ultrasound 。 Yin Yingwu of the company used carbon nanotubes or modified carbon nanotubes as a new catalyst to catalyze the oxidation of bisglyphosate to prepare glyphosate; Wang Youren et al.
also developed a preparation method for glyphosate, which includes using hydrogen peroxide to catalyze the oxidation of bisglyphosate raw materials to obtain an oxidizing solution, and then adding a sulfide reducing agent with weak reducibility to the oxidation solution to consume excess hydrogen peroxide in the oxidation reaction, and then adding ferrous sulfate for reduction, and then separated and dried
.

Chen Tianyun of Anhui Huaxing Chemical Co.
, Ltd.
used water as a solvent, added bisglyphosate, dilute nitric acid and activated carbon catalyst loaded with transition metals or salts under stirring conditions, and introduced a gas containing molecular oxygen at low pressure to heat the reaction; After the end of the reaction, thermal filtration and filtrate cooling crystallization to precipitate glyphosate
.

Zhejiang University of Technology Laihuqin et al.
used bisglyphosate as raw material, oxygen as oxidant, and highly active palladium carbon as catalyst to oxidize glyphosate
.
Under the condition that the mass ratio of bisglyphosate to catalyst was 1:0.
01, the reaction temperature was 95°C, and the reaction pressure was 0.
25 MPa, oxygen was stopped after 3 h of heat preservation.
Then the shielding gas is introduced, and glyphosate is obtained after heating and pressurizing the reaction for a period of time, and most of the palladium ions lost in the solution are reduced, the reaction yield is 94.
6%, and the purity is 95.
6%
。
Wang Hongming of Anhui Guoxing Biochemical Co.
, Ltd.
and others have developed a method for preparing glyphosate by catalytic oxidation of bisglyphosate under ultraviolet light source irradiation, diglyphosate, self-made loaded activated carbon catalyst, water, mixed evenly according to a certain proportion, then driven into the reactor irradiated by ultraviolet light, into the air flow, fully reacted at a certain pressure and temperature, after 3~6h, ammonia gas is fully reacted to obtain ammoniated liquid, and the catalyst is recovered for the next application
。 The ammoniation solution is injected into the crystal kettle and the concentrated sulfuric acid is added dropwise to adjust the pH value at 1.
0~1.
8, the temperature is lowered to 0~5 °C, and the crystallization is fully acidified at this temperature, and glyphosate crystals
are obtained after filtration and washing.
The method of the present invention has high yield, high product purity, few by-products, and fast
reaction speed.


IDA route started late in China, but has been developed rapidly in recent years, compared with the glycine route, it has the advantages
of simple process route, good product quality, low "three wastes" and less by-products 。 Although the hydrocyanic acid-IDA-glyphosate route using hydrocyanic acid as raw material has achieved industrial production in China, it still needs a process optimization process, the main reason is that the hydrocyanic acid synthesized in China is not derived from acrylonitrile by-products, but is synthesized from natural gas and ammonia, and its concentration is low and needs to be concentrated to meet the needs of
synthesis.
In addition, the technology has not yet achieved industrial large-scale production, which makes the price of IDA high, so that the production cost of glyphosate is high, resulting in the advantages of the process not being fully utilized
.
Once this problem is solved, the IDA route with hydrocyanic acid as raw material will become the dominant route
for glyphosate synthesis in China.