Issue 2, 2014 - Research progress on glyphosate synthesis process in China

Research progress of glyphosate synthesis process in China

□ Yan Feng

Glyphosate, chemically known as N-phosphorylmethylglycine (PMG), is a broad-spectrum organophosphorus herbicide
.
In recent years, with the large-scale planting of genetically modified glyphosate-resistant crops such as soybeans, corn, cotton, etc.
, the market demand for glyphosate has continued to increase
.
At present, the industrial production methods of glyphosate mainly include glycine
method and iminodiacetic acid (IDA).

1.
Glycine method

Glycine method is currently the most important method
for the production of glyphosate in China.
First, glycine is synthesized from chloroacetic acid or hydrocyanic acid, and glycine is then synthesized by reacting with other raw materials
.
According to the raw materials used, the glycine route can be divided into chloromethyl phosphate method and phosphite alkyl ester method, the former has been eliminated, the latter is glycine, paraformaldehyde and phosphite alkyl ester as raw materials, after addition, hydrolysis reaction synthesis of glyphosate
.
According to the different alkyl groups in phosphite alkyl esters, the method can be divided into trimethyl phosphite method, diethyl phosphite method and dimethyl phosphite method
.
Dimethyl phosphite method is currently the main process method for the production of glyphosate in China, and its output accounts for 90%
of the alkyl ester method.
However, there are also some problems with this method, such as the large use of triethylamine and methanol increases the cost of solvent recovery and environmental pressure, and the yield of the product needs to be further improved (currently about 80%)
.

Wang Wei of Zhejiang Xinan Chemical Group Co.
, Ltd.
and others developed a continuous crystallization method
for glyphosate.
After neutralizing the hydrolysate in glyphosate prepared by alkyl ester method, it is continuously fed to the circulating crystallizer for crystallization, the average residence time in the crystallizer is 0.
5~24h, the crystallization temperature is 0~40 °C, and the crystallization solution is continuously discharged for separation
.
This method effectively improves the stability and automation of glyphosate crystallization in the production process, and reduces the production cost
.

Shanghai Taihe Chemical Co.
, Ltd.
Zhu Zhengjiang and others innovatively use hydrogen chloride instead of hydrochloric acid for hydrolysis
.
Compared with the two processes, hydrogen chloride hydrolysis has the advantages
of 65% higher than hydrochloric acid hydrolysis of by-product chloromethane, 50% lower energy consumption for desolubilization, and 27% less wastewater.

Huang Ming et al.
of Beijing Tsinghua Ziguang Yingli Chemical Technology Co.
, Ltd.
put glycine and paraformaldehyde into the depolymerization and condensation reaction of monohydryl/tertiary amine system at the same time according to the optimized ratio, and then condensation reaction with the optimized proportion of dialkyl phosphite esters at the optimized pH value, recovery of monohydryl alcohols and tertiary amines, and then acidification and hydrolysis at controlled temperature, and removal or oxidation of formaldehyde at the same time of acidification hydrolysis, precipitation of glyphosate, and the mother liquor as an acid directly applied
.

Song Qinhua of Jiangsu Thorpe (Group) Co.
, Ltd.
added glycine and polyoxymethylene to form N, N-dihydroxymethylolglycine in methanol solvent under the action of catalyst KOH; N, N-dimethylolglycine polymerizes with dimethyl phosphite to generate glyphosate methyl ester; Hydrochloric acid was added to the reaction solution for acidolysis to generate glyphosate and formaldehyde.

Distillation of deacidified methanol, deacidification under reduced pressure at a temperature of 115 °C, filtration crystallization to obtain solid glyphosate, mother liquor does not contain sodium chloride, the main ingredient is glyphosate and glyphosate potassium salt, can be used as potassium fertilizer
.

2.
Iminodiacetic acid method

The iminodiacetic acid method is to first synthesize iminodiacetic acid (IDA), and then react IDA with formaldehyde, phosphorous acid (or phosphorous trichloride instead of phosphorous acid) to generate bisglyphosate, and bisglyphosate is oxidized to obtain glyphosate
.
This method is currently the most advanced production process in the world, producing more than 75% of the total production of glyphosate, which is the route adopted by Monsanto
, the world's largest producer of glyphosate.
There are two key points of this process route: one is the synthesis of the intermediate product iminodiacetic acid, and the other is the oxidation
of bisglyphosate.

1.
Synthesis of intermediate product IDA The hydrocyanic acid method is the main method for synthesizing IDA in the world, using hydrocyanic acid, formaldehyde and methenamine as raw materials to synthesize iminodiacetonitrile, and then hydrolyzed and acidified to obtain IDA
.
This method is suitable for large-scale production, and the production efficiency is high, and the purity of the product can reach 95%.

At present, the raw material hydrocyanic acid used abroad mainly comes from the by-product tail gas of the production of acrylonitrile, and the cost of raw materials is low
.
Due to the source of hydrocyanic acid, this method has not been widely promoted and applied
in China.
The Sichuan Research Institute of Chemical Industry and the Chongqing Ziguang Chemical Plant have mastered the technology of producing hydrocyanic acid from natural gas and have industrialized production
.

The diethanolamine method is to prepare IDA
by catalytic dehydrogenation using diethanolamine and sodium hydroxide as raw materials.
When using amorphous alloys as catalysts and using bipolar membrane electroosmosis technology to synthesize IDA, the conversion rate of diethanolamine is as high as 99%, and the yield of IDA can reach 95%.

The catalyst can be reused
.
However, due to the small amount of raw material diethanolamine and the high cost of imports, large-scale industrial production is limited
.

The nitrogen triacetic acid method is to obtain nitrogen triacetic acid by reacting chloroacetic acid and ammonia, and then obtaining IDA
by oxidative formaldehyde.
The advantages of this method are low raw material price, simple route and high product yield, and the disadvantage is that the product yield is too sensitive to reaction conditions, and large-scale industrial production
has not yet been realized.

2.
Preparation of glyphosate by oxidation of bisglyphosate Hydrogen peroxide oxidation method is a commonly used industrial production method in China, the synthesis of glyphosate by this method has the characteristics of simple post-treatment and high yield, the disadvantage is that the amount of hydrogen peroxide is large, the oxidation temperature is difficult to control, in addition, the metal salt content in the reaction mother liquor is large, which is not only difficult to separate, but also reduces the yield and purity
of glyphosate.
Electrolytic oxidation has not yet been industrialized
.

The catalytic oxidation of glyphosate generally uses oxygen or oxygen-containing gas as an oxidant, and glyphosate is synthesized from bisglyphosate
under the action of a catalyst.
This method belongs to the category of green chemistry, and the product yield and purity are high
.
The selection, preparation and recycling of efficient catalysts are key
to this process.

3.
Technological progress Zhou Shuguang of East China University of Science and Technology and others synthesized glyphosate by catalytic oxidation reaction using bisglyphosate
and oxygen as raw materials and activated carbon as catalysts.
The results show that when the mass ratio of catalyst to bisglyphosate is 0.
188, the reaction temperature is 45°C, and the reaction pressure is 0.
5MPa for 5h, the total yield of glyphosate can reach 97.
1%.


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


In the presence of catalyst tungstate, Wang Wei et al.
of Zhejiang Xin'an Chemical Group Co.
, Ltd.
added alkyl hydroanthraquinone or hydroanthraquinone dissolved in organic solvent to the bisglyphosate-water system, and then introduced oxygen-containing gas into the reaction system for reaction
.
The obtained reaction solution was used as a reactant, and the catalyst ferrous sulfate or sodium sulfite was added for decarboxylation reaction to obtain glyphosate crystals
.

Guo Yulai of Beijing Tsinghua Unigroup Yingli Chemical Technology Co.
, Ltd.
directly used air or oxygen as an oxidant, and oxidized bisglyphosate to glyphosate
with high yield under the combined catalysis of activated carbon or carbon nanotubes and ultrasonic ultrasound.

Yang Yongjun of Chenzhou Sun Art Platinum Industry Co.
, Ltd.
adsorbed chloropalladite acid and two metal additives M solution to the modified carrier carbon in turn, reduced washing and drying to prepare Pd-M/C three-way alloy catalyst, and prepared glyphosate (PMG) by catalyzing oxidation of bisglyphosate (PMIDA) with the participation of Pd-M/C, PMIDA conversion rate was 100%, and PMG yield was 98~99%.


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 is 1:0.
01, the reaction temperature is 95 °C, and the reaction pressure is 0.
25MPa, oxygen is stopped after 3h of heat preservation; then protective gas is introduced, and glyphosate
is obtained after heating and pressurizing for a period of time.

Wang Hongming of Anhui Guoxing Biochemical Co.
, Ltd.
mixed bisglyphosate, self-made loaded activated carbon catalyst and water in a certain proportion and then punched into a reactor irradiated by ultraviolet light, passed into the air flow, fully reacted under a certain pressure and temperature for 3~6h, and filtered ammonia liquid after full reaction of ammonia gas, and recovered the catalyst for the next use
.
The ammoniation solution was injected into the crystal kettle and concentrated sulfuric acid was added dropwise to adjust the pH value to 1.
0~1.
8, cooled to 0~5 °C, fully acidified crystallization, and glyphosate crystals
were obtained after filtering and washing.
In addition, Li Jian et al.
of the company developed a method
for catalyzing the oxidation of bisglyphosate to prepare glyphosate under microwave action.

3.
Concluding remarks

Glycine route is currently the main process of synthesis of glyphosate in China, after years of development, its process operation conditions are mature, product yield and quality have also been greatly improved, the future development focus is to simplify the process route, reduce the amount of solvent use and develop new and effective solvent recovery methods, reduce environmental pollution
.

Compared with the glycine route, the IDA route has the advantages of simple process route, good product quality, low three wastes and less by-products, and has developed rapidly
abroad.
Although the hydrocyanate-IDA-glyphosate route has achieved industrial production in China, its large-scale development still requires a process, mainly because 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 requirements
.
In addition, due to the high price of the raw material hydrocyanic acid, the production cost of glyphosate is high
.
Once this problem is solved, the IDA route based on hydrocyanic acid will develop
rapidly.