Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF N-PHOSPHONOMETHYL GLYCINE

Abstract

An improved process for the preparation of N-phosphonomethyl glycine : The present invention provides an improved process for the preparation of N-phosphonomethyl glycine by treating a tribasic salt of N-phosphonomethyl glycine with hydrochloric acid followed by electrolysis by using inter polymer type cation membrane and anion exchange membrane . During electrolysis , the said polymer type cation membrane and anion exchange membrane is capable of separating the alkaline salts obtained from the reaction of tribasic salt of N-phosphonomethyl glycine and HCL , to facilitate separation of a solution of N-phosphonomethyl glycine . Recovery of N-phosphonomethyl glycine can be effected by conventional method from the separated solution.

Full Text

The present invention relates to an improved process for the preparation of N-phosphonomethyl glycine. The present invention particularly relates to an improved process for the preparation of N-phosphonorhethyl glycine, from its alkali metal salt (tri basic) by the application of acid neutralisation followed by electrodialysis using perm selective ion exchange membranes. N-phosphonomethyl glycine commonly known as Glyphosate in the form of its isopropyi amine salt, is a widely used product in agriculture as a herbicide. A large number of methods for the manufacture of N-phosphonomethyl glycine are known. Some of the production methods result in the formation of tribasic salt (alkali metal salt) of N-phosphonomethyl glycine, warranting the isolation of free and pure N-phosphonomethyl glycine to meet the specification. Thus there is a need for an appropriate method for the isolation of N-phosphonomethyl glycine from its aqueous alkaline solutions. Various processes are known for the production of N-phosphonomethyl glycine and one of the methods of choice being the catalytic oxidative dehydrogenation of the corresponding N-phosphonomethyl ethanolamine in presence of alkali metal hydroxide and Raney copper catalyst as mentioned in US 4782183, WO 9206069, US 4810426, EP 0945428 and US 5225592, where in a suitably substituted amino alcohol derivative is converted to the corresponding amino carboxylic acid metal salt. (Formula Removed) M = Alkali metal or Alkaline earth metal All patented methods mentioned above invariably end up in alkali metal salt (tri basic salt) of N-phosphonomethyl glycine. Thus a means for isolating and purifying the N-phosphonomethyl glycine from the aqueous alkaline solution in high purity and high yield is an important and vital issue and is in great demand. Therefore the N- phosphonomethyl glycine must be isolated and purified to meet the specification by contacting either with an acid or by any other means of separation. In the acid contacting method a minimum of three moles of metal halide per mole of N-phosphonomethyl glycine results warranting separation of metal halides. In a patented disclosure of US 4221583 N-phosphonomethyl glycine was separated using an ion-exchange resin after hydrolysis of the corresponding N-phosphonomethyl glycinonitrile with hydrochloric acid or sodium hydroxide. In another patented disclosure of Showa Denko (EP 0806428) N-phosphonomethyl glycine was isolated from its aqueous alkali metal salt/alkaline earth metal salt by acid neutralisation to pH 3.5 or higher there by precipitated salts are removed, followed by readjusting the pH to 2.5 or lower to crystallise out N-phosphonomethyl glycine. In another patented invention by Zeneca (WO 9705149) the product N-phosphonomethyl glycine is isolated from its aqueous mixture or from an effluent stream by complexing with Fe(lll) salts followed by releasing the product by basification with alkali. The reported patented processes suffer from various practical operational problems such as repeated pH adjustments, concentrations and filtrations for the removal of major portion of salt from the final product (EP 0806428), the ion-exchange resin isolation of N-phosphonomethyl glycinonitrile from its salts employing high pressure liquid chromatography ion-exchange resins (US 4221583) or dealing with high dilutions such as 1.89%, 1.41% and 1.49% (EP 0413672A2). The iron complexation method (WO 9705149) is likely to generate an additional effluent ferric oxide and requires a separation technique to isolate pure N-phosphonomethyl glycine from the salt. These results in less product recovery and above all the inorganic salts generated may contain the glyphosate as contaminant posing effluent disposal problem. The main objective of the present invention is to provide an improved process for the preparation of N-phosphonomethyl glycine, which obviated the drawbacks as detailed above. Another object of the present invention is to provide an improved method for the preparation of N-phosphonomethyl glycine from its aqueous alkali salt/alkaline earth metal salt by contacting with an acid followed by electrodialysis to yield N-phosphonomethyl glycine totally devoid of any metal salt, in high yield and high purity. The aqueous metal salt may be sodium or potassium or a mixture there of. Yet another objective of the present invention is to reduce the cost of production due to high energy inputs required for concentration of large volumes of filtrates containing N-phosphonomethyl glycine by electrodialysis, where in simultaneous transportation of ions is accompanied by large amounts of water, there by resulting in concentrated glyphosate solution. Still another objective of the invention is to improve the isolation yield and purity of glyphosate by removing all the metal halides/metal carbonates by selectively transporting them through the perm selective membranes by electrodialysis. Yet another objective of the present invention is to obtain pure aqueous metal halide solutions devoid of any N-phosphonomethyl glycine contamination, with which a salable commodity can be obtained. Accordingly the present invention provides an improved process for the preparation of N-phosphonomethyl glycine , which comprises of treating a tribasic salt of N-phosphonomethyl glycine with hydrochloric acid followed by electrolysis by using inter polymer type cation membrane and anion exchange membrane such as herein described which is capable of separating the alkaline salts through it, by applying electric potential in the range of 10 - 20 volts , in the temperature range of 20 - 50 ° C for a period of 3-8 hours , to get a solution of N-phosphonomethyl glycine and recovering N-phosphonomethyl glycine by conventional method as herein described. In an embodiment of the present invention the acid used to neutralize the tribasic salt may be such as hydrochloric acid. In an another embodiment of the present invention the electrodialysis may be effected by applying electric potential in the range of 10-20 volts, preferably in the range of 15 volts; effectively 1.5 volts DC per cell pair, i.e. set of anion and cation exchange membrane in the electrodialysis stack. In yet another embodiment of the invention the electrodialysis of the mixture may be effected by using membrane, which is capable of dialysing the alkali/alkaline earth metal salts through it, such as inter polymer type cation and anion exchange membranes (IP 124573) In yet another embodiment, the recovery of N-phosphonomethyl glycine may be effected by per evaporation, concentration or crystallisation or by combination thereof. In a feature of the invention separation of N-phosphonomethyl glycine from its alkali metal/alkaline earth metal salt solution may be effected by neutralisation with acid followed by electrodialysis of the product mixture containing the corresponding metal halides etc., as contaminants at an ambient pressure and temperature in the range of 20-50°C. In accordance with the present invention N-phosphonomethyl glycine is isolated and purified in high yield and high purity. In the inventive method the neutralized mass of tribasic salt of N-phosphonomethyl glycine is subjected to acidification followed by electrodialysis there by the entire metal halide salts will be selectively transported/removed leaving highly concentrated mass of N-phosphonomethyl glycine completely devoid of metal halides. Per evaporation or crystallisation of the concentrated mass provides the N-phosphonomethyl glycine. The electrodialysis unit consists of a 20 compartment cell with an effective cross sectional area of 300 square cm (25 X 12 cm), designed and fabricated in house. Stainless steel sheet was used as a cathode, where as an activated triple precious metal oxide coated titanium was used as an anode. The electrodes were housed in a rigid PVC chamber with built in flow distribution inlet and outlet tubes and are protected with a thin gasket of non-conducting material designed in such a fashion to handle 4 independent flows i.e., anolyte, catholyte, treated and concentrated solution with out inter mixing at any time of operation. Anolyte is the solution, which is circulated in the anode compartment and catholyte is a solution circulated in the cathode compartment. Usually 0.1 N solution of sodium sulphate solution is used as anolyte and catholyte and generally any chloride salt solutions will be avoided as chlorine will be liberated at the anode which in turn effects the membrane facing the anode. Treated solution refers to the sample desalted by the application of electrodialysis where as the concentrate refers to the stream wherein the desalted metal halides will be collected, hence referred to as the concentrated (in metal halide salts). Inter polymer type cation and anion exchange membranes manufactured as for the literature methods (IP 124573, CA 77 (1972), 760273), were packed alternately in between two electrode housings along with gaskets having built in flow arrangement and spacing. The reaction is conducted at ambient pressure and proceeds satisfactorily at temperature between 20-50°C , the preferred temperature being 38-40°C. Metal halide salts such as sodium chloride, potassium chloride etc., in the range of 1-25% w/w were effectively removed. More the concentration of salt in the product mixture faster the transportation of the metal halide and serves the dual purpose i.e., apart from the salt removal simultaneous concentration of the aqueous N- phosphonomethyl glycine solution also is effected. Under this conditions the reaction times up to 3-8 hours is common but 5 hours is generally sufficient to complete the transportation of the salt. After an extensive study the inventors have optimized the parameters such that the transportation of N-phosphonomethyl glycine is minimized or nil along with the metal halide salts. The completion of the transportation is monitored by chemical analysis or HPLC analysis of the treated sample or line sample. The process for the elimination/transportation of metal halides/carbonates etc., from the aqueous solution of N-phosphonomethyl glycine is not limited for example, given the subject, the aqueous solution may be obtained in a production process or in a purification process there of N-phosphonomethyl glycine. The present invention employs the electrodialysis technique for the first time for separating the metal halide contamination from the glyphosate solutions, which has distinct advantage over the existing methods resulting in a cost effective process for the glyphosate manufacture/isolation. The invention now will be presented in detail in the following example. However the example should not be construed as limiting. The feed "N-phosphonomethyl glycine tri basic salt" is obtained by following the reported method (EP 0620209). Many a number of experiments were carried out using aqueous sodium hydroxide, aqueous potassium hydroxide as the base, resulting in N-phosphonomethyl glycine tri basic salt of varying concentration of metal halide (obtained on acidification). Example 1: An aqueous solution of dipotassium salt of N-phosphonomethyl ethanolamine (0.308moles) and Raney Copper (15gms, 45-50% moisture) were introduced into a 500mL capacity Hastelloy-B2 autoclave equipped with a mechanical stirrer, condenser and a vent. The contents were stirred and degassed by pressurizing the reactor with inert gas (Helium/Nitrogen) two times and all the vents were closed properly. The contents were then heated to a temperature of 168-170°C allowing the pressure to rise to 15kg/cm2 by adjusting the vent of the reactor. At the end of the reaction (Hydrogen liberation stops) the reactor contents were cooled, discharged, and carefully filtered. The precipitated mass (recovered catalyst) was recycled in subsequent reactions. The filtrate containing the N-phosphonomethyl glycine tri basic salt (potassium) was estimated for its content by complexometry and subjected for separation. The alkaline filtrate was brought to pH less than 3 at 25°C by contacting with hydrochloric acid. The acid solution containing N-phosphonomethyl glycine and alkali metal halide (KCI) was transferred to the electrodialysis unit and the metal halides were removed by applying electric potential. During the process of electrodialysis some of the water gets removed (transported along with the metal ions) making the aqueous solution containing the glyphosate highly concentrated. This concentrated solution can be subjected for crystallisation or per evaporated to collect the N-phosphonomethyl glycine. The product is obtained in high purity and high yield. Example 2: The acid solution containing N-phosphonomethyl glycine and alkali metal halide (KCI) (580 gms., 6.34% glyphosate content, 16.535% potassium chloride content) was diluted with 500 gms. of fresh water and electrodialyzed by the application of an external electric potential of 15 volts, effectively 1.5 volts DC for each cell pair (anion and cation membrane) for a period of 6 hours. At the end of the operation 776.5 gms. of treated sample (desalted sample) with 3.99% glyphosate and 0.16% potassium chloride was obtained. Yield: 84.23%. Example 3: The acid solution containing N-phosphonomethyl glycine and alkali metal halide (KCI)( 1155 gms., 6.34% glyphosate content, 16.535% potassium chloride content)was electrodialyzed by the application of an external electric potential of 18 volts, effectively 1.8 volts DC for each cell pair (anion and cation membrane) for a period of 7 hours. At the end of the operation 750 gms. of treated sample (desalted sample) with 8.34 % glyphosate and 0.17 % potassium chloride was obtained. Yield: 85.43 %. Example 4: The acid solution containing N-phosphonomethyl glycine and alkali metal halide (KCI) (930 gms., 6.34% glyphosate content, 16.535% potassium chloride content) was diluted with 226 gms. of fresh water and electrodialyzed by the application of an external electric potential of 18 volts, effectively 1.8 volts DC for each cell pair (anion and cation membrane) for a period of 3.5 hours. At the end of the operation 763 gms. of treated sample (desalted sample) with 6.53 % glyphosate and 0.49 % potassium chloride was obtained. Yield: 84.5 %. Example 5 The acid solution containing N-phosphonomethyl glycine and alkali metal halide (KCI) (916 gms., 10.26 % glyphosate content, 13.58 % potassium chloride content) was diluted with 216 gms. of fresh water and electrodialyzed by the application of an external electric potential of 10 volts, effectively 1.0 volts DC for each cell pair (anion and cation membrane) for a period of 2.1 hours. At the end of the operation 819 gms. of treated sample (desalted sample) with 11.5 % glyphosate and NIL potassium chloride content was obtained. Yield: 90.48 %. Example 6: The acid solution containing N-phosphonomethyl glycine and alkali metal halide (KCI) (1630 gms., 6.422 % glyphosate content, 13.28 % potassium chloride content) was electrodialyzed by the application of an external electric potential of 12 volts, effectively 1.2 volts DC for each cell pair (anion and cation membrane) for a period of 3 hours. At the end of the operation 848 gms. of treated sample (desalted sample) with 11.23 % glyphosate and 1.7 % potassium chloride content was obtained. Yield: 90.94 %. Example 7 The acid solution containing N-phosphonomethyl glycine and alkali metal halide (KCI) (1350 gms., 7.51 % glyphosate content, 23.03 % potassium chloride content) was electrodialyzed by the application of an external electric potential of 12 volts, effectively 1.2 volts DC for each cell pair (anion and cation membrane) for a period of 2.7 hours. At the end of the operation 807 gms. of treated sample (desalted sample) with 9.11 % glyphosate and NIL potassium chloride content was obtained. Yield: 72.5 %. Example 8: The acid solution containing N-phosphonomethyl glycine and alkali metal halide (KCI) ( 1133 gms., 7.89 % glyphosate content, 21.66 % potassium chloride content) was electrodialyzed by the application of an external electric potential of 12 volts, effectively 1.2 volts DC for each cell pair (anion and cation membrane) for a period of 2.5 hours. At the end of the operation 718 gms. of treated sample (desalted sample) with 9.27 % glyphosate and 0.03 % potassium chloride was obtained. Yield: 74.4 %. Example 9: The acid solution containing N-phosphonomethyl glycine and alkali metal halide (KCI) (1090 gms., 6.73 % glyphosate content, 14.82 % potassium chloride content) was electrodialyzed by the application of an external electric potential of 10 volts, effectively 1.0 volts DC for each cell pair (anion and cation membrane) for a period of 2.25 hours. At the end of the operation 574 gms. of treated sample (desalted sample) with 8.96 % glyphosate and NIL potassium chloride was obtained. Yield: 70 %. Advantages: The advantage of the present invention is that the N-phosphonomethyl glycine obtained by electrodialysis is totally devoid of any metal salt contamination. Another advantage of the present invention is that the metal halide solution obtained is devoid of any N-phosphonomethyl glycine contamination, thus making it a salable commodity. Yet another advantage of the invention is that by electrodialysis metal salts in the range of 1-25% can be efficiently separated from aqueous streams of N-phosphonomethyl glycine. Still at another advantage of the invention is that the electrodialysis operation serves the dual purpose i.e., apart from metal halide salt removal simultaneous concentration of N-phosphonomethyl glycine occurs, thus reducing the cost incurred for concentration of glyphosate solution. We Claim: 1. An improved process for the preparation of N-phosphonomethyl glycine , which comprises of treating a tribasic salt of N-phosphonomethyl glycine with hydrochloric acid followed by dia electrolysis by using inter polymer type cation membrane and anion exchange membrane such as herein described which is capable of separating the alkaline salts through it, by applying electric potential in the range of 10 - 20 volts , in the temperature range of 20 - 50 0 C for a period of 3-8 hours , to get a solution of N-phosphonomethyl glycine and recovering N-phosphonomethyl glycine by conventional method as herein described. 2. An improved process as claimed in claim 1 wherein electrolysis is effected preferably at 15 volts. 3. An improved process as claimed in claims 1 -2 wherein the recovery of N-phosphonomethyl glycine is carried outby evaporation or crystallization. 4. An improved process for the preparation of N-phosphonomethyl glycine as herein described with reference to the examples.

Documents:

1223-del-2003-abstract.pdf

1223-del-2003-claims.pdf

1223-del-2003-correspondence-others.pdf

1223-del-2003-correspondence-po.pdf

1223-del-2003-description (complete).pdf

1223-del-2003-form-1.pdf

1223-del-2003-form-19.pdf

1223-del-2003-form-2.pdf

1223-del-2003-form-3.pdf