FORM 2
THE PATENTS ACT, 1970 (39 OF 1970)
COMPLETE SPECIFICATION
[SECTION 10; RULE 13]
"A METHOD AND APPARATUS FOR CONTINTJOS MANUFACTURING
OF ACEPHATE"
APPLICANT: Laxmi Organic Industries Ltd.
NATIONALITY: Indian Company
ADDRESS: Chandermukhi 3rd floor, Nariman Point, Mumbai - 400 021,
India,
THE FOLLOWING SPECIFICATION DESCRIBES THE NATURE OF THE INVENTION

FIELD OF INVENTION
The present invention relates to a method and an apparatus for continuous manufacturing of Acephate. More particularly, the present invention relates to a method and apparatus for continuous manufacturing of Acephate by acetylation of Methamidophos (MMP) using Ketene gas in presence of Methylene Dichloride (MDC) as a solvent and p-Toluenesulphonic acid (PTSA) as a catalyst.
BACKGROUND OF INVENTION
Acephate is the acetylated derivative of the insecticide Methamidophos (MMP) having the formula and TUPAC name as given below:

Acephate is an efficient, low mammalian toxicity (30 times lower than MMP), low residue, broad spectrum pesticide which is primarily used inter alia for rice, cotton, vegetables and fruits. It has good control effect and is an ideal replacement for highly toxic pesticides such as MMP, Parathione, Methyl parathione and Monocrotophos that are banned world over keeping in mind the social and economic development.

Most of the manufacturing processes reported till date use O-O-Dimethyl Thiophosphamide, which is catalytically isomerized to O-S-Dimethyl Thiophosphamide (also known as Methamidophos/MMP). MMP is used as raw material for obtaining Acephate. Acephate is generally obtained by acetylation of O-S-Dimethyl Thiophosphamide (Methamidophos/MMP). The acetylation is effected using acetylating agents like acetyl chloride and acetic anhydride. Further, in these processes, the use of acetyl chloride and acetic anhydride produces hydrochloric acid and acetic acid respectively as by-products, which are required to be removed by means of additional steps of neutralization with alkali, extraction with organic solvents and isolation right up to the final quality product. These additional steps not only add to the product cost, but also consume more time and material. In the aforesaid step of neutralization, water is generally used to prepare alkali solution. The solubility of Acephate in water itself leaves up to 2% of the product in the effluent stream, leading to the pollution in environment. Ketene may also be used as an acetylating agent. However, Ketene exists in a gas form and compression of Ketene would pose a major problem during the production of Acephate as it has a strong tendency to polymerize into dry form which results in clogging of the process lines. Polymerisation can however be reduced by compressing Ketene using liquid piston type rotary gas blowers; but, the particular approach would lead to loss of part of the feed liquids. The drawbacks associated with the compression of Ketene also include requirement of extra equipment for separation of Ketene from its polymers and heavy foaming that interferes in phase separation.
Several batch processes have been disclosed in the prior art for the manufacture of Acephate using Ketene. However, the batch processes of the prior art involve

cumbersome operational steps leading to limited production capacities. Further, any batch process has limitations of production capacity, equipment line-up issues and production time frame schedule, which adds to the cost.
Chinese Patent No. 102060872 discloses a continuous production method of Acephate by acetylation of Methamidophos (MMP) with acetic anhydride by continuous mode. Though the said document addresses the constraints of low production capacity, exhibiting voluminous production and comparative cost reduction, the operational complexities of neutralization with alkali, solvent extraction and effluent management have remained unsolved.
OBJECT OF INVENTION
Therefore, the main object of the present invention is to provide a method and set of equipments for the continuous manufacturing of Acephate using Ketene, which overcomes the limitations/defects of the prior art.
The present invention proposes the hassle free and direct absorption of the Ketene gas into the liquid reactant (MMP-MDC-PTSA solution) followed by reaction of Ketene gas with MMP-MDC-PTSA solution with effective heat and mass transfer. The present invention also proposes to achieve maximum per pass utilisation/consumption of Ketene.
SUMMARY OF THE INVENTION
The present invention relates to a method for continuous manufacturing of Acephate comprising of acetylation of O-S-Dimethyl Thiophosphamide

(Methamidophos/MMP) by absorption of Ketene under vacuum in presence of p-Toluene sulphonic acid (PTSA) as catalyst and Methylene dichloride (MDC) as solvent and an apparatus for continuous production of Acephate comprising two or more reaction vessels connected in series or parallel, each having a device to create vacuum; inlets to receive unreacted or partly reacted mixture of MMP, MDC and PTSA and Ketene; and an outlet.
DESCRIPTION OF THE INVENTION
The invention is described with reference to the drawings accompanying this specification wherein numerals are used to denote the parts and wherein, the figures only illustrate the invention and in no way limit the said invention.
The present invention provides a method for continuous manufacture of Acephate using Ketene and an apparatus for the same. MMP is used as the starting material for obtaining Acephate and Ketene having purity of at least 90% is used as the acetylating agent.
Figure 1 shows the process flow diagram showing convenient arrangement of the equipment used for the continuous manufacture of Acephate.
With reference to Figure 1, there is provided an arrangement of the equipments used for the continuous manufacturing of Acephate. In a preferred embodiment, a liquid ejector (8A) is mounted over a liquid ring vacuum pump (8B) which is connected to a gas-liquid separator (8C). The liquid ejector (8A) is provided with two inlets - one

inlet for Ketene gas entering the liquid ejector through stream (7) and the other inlet (6A) for entry of mixture of Methamidophos (MMP), Methylene Dichloride (MDC) and p-Toluenesulphonic acid (PTSA) solution (hereinafter referred to as "the feed solution") entering the ejector (8A) from the cooler (5) via pipe (6). The liquid ring vacuum pump (8B) has an inlet (6B) for entry of the feed solution from the cooler (5) via pipe (6) and an outlet (9A) connecting the liquid ring vacuum pump (8B) to the gas-liquid ejector (8C). The gas-liquid separator (8C) has two outlets (9A and 9B), one at the bottom for removing the partially converted product (i.e. Acephate) and MDC through stream (9B) opening into the gas inducing reactor (GIR) (8D) and another stream (9C) at the top. directing unreacted Ketene gas into the impeller of the GIR (8D). Since the reaction kinetics of the particular acetylation reaction slows down towards the end of the reaction, balance unconverted reaction mass is sent to the said GIR (8D). Traces of unreacted Ketene gas go to a packed column (2) through stream (3). The packed column (2) is provided with an inlet for fresh feed solution, entering at top through stream (1). It has two outgoing streams viz. a top stream (10) and a bottom stream (4). The top stream (10) carries the waste gases and traces of unreacted Ketene gas to final weak acid scrubber column. The Ketene scrubber (11) is provided with an inlet for water entering through stream (12) and an outlet (14) for removal of weak acetic acid.
Bottom stream (4) of the packed column (2) carries the feed solution and partly formed Acephate to the pump (13) which pumps the complete solution back to the liquid ejector (8A) and the liquid ring vacuum pump (8B), through a cooler (5).

Vacuum is developed within the liquid ejector (8A) with the aid of the pressure energy associated with the motive fluid. Here, unreacted feed solution fed through stream (6) acts as the motive fluid. Ketene gas as pure as 95%, is drawn into the liquid ejector (8A) through stream (7). Ketene is instantaneously absorbed (co-currently) into the feed solution, and upon the intimate contact between the two fluids, leads to the initiation of the acetylation reaction. Cooled feed solution from the cooler (5) is also partly fed to the liquid ring vacuum pump (8B) through stream (6) via inlet (6B). It reinstates itself as the ring liquid or the sealant to liquid ring vacuum pump (8B). With the aid of vapor pressure of the ring liquid, vacuum is developed within the pump. As a result, unreacted feed solution along with Ketene from the liquid ejector (8A) is further sucked and dispersed into the liquid ring vacuum pump (8B) (co-currently). Upon intense intimate contact between gas and liquid phase, acetylation reaction happens within liquid ring vacuum pump (8B). Stream (9A), contains mixture of partly converted feed solution and unreacted Ketene gas coming out from liquid ring vacuum pump (8B), which enters the gas-liquid separator (8C). Here, liquid and gas phases are separated out such that the partially converted acephate alongwith excess MDC exits the gas-liquid separator (8C) through stream (9B) at the bottom and the unreacted ketene gas exits the gas-liquid separator (8C) stream (9C) at the top. As the acetylation reaction proceeds, the rate of reaction slows down, thus, kinetics for the balance part of the reaction is pushed towards right by pursuing it in a gas inducing reactor (GIR) (8D) at a relatively elevated temperature. Unreacted Ketene gas exiting the gas liquid separator (8C) through stream (9C) is bubbled into the gas inducing reactor (8D) containing liquid (partially reacted acephate and MDC), with the aid of the gas

inducing impeller. The impeller speed is so adjusted, that static and dynamic pressures are overcome and sufficient level of vacuum is developed at the tip of the impeller blade. By virtue of this, Ketene is sucked into the gas inducing reactor (8D). Volume for the said gas inducing reactor (8D) is maintained to the level of sufficient residence time in order to ensure complete conversion of MMP. Since the reaction is pursued at relatively elevated temperatures, MDC present within the
solution starts vaporizing out. This vaporized MDC is condensed and refluxed back

into the system with the aid of a reflux condenser (8E), thereby keeping MDC solvent losses to minimum. Acephate so formed remains in dissolved form in the solvent MDC and is drawn out continuously from the bottom of the gas inducing reactor (8D) through a U-loop arrangement in stream (9D).
Traces of unreacted Ketene gas coming out from the gas inducing reactor (8D) through stream (3) are subsequently absorbed (counter-currently) within the fresh feed solution entering the packed column (2) through stream(l). The flow of ketene and the feed solution entering the packed column is in a counter current fashion. Partly converted feed solution goes out from the bottom of the packed column (2) through stream (4) and is recycled to the ring liquid to the liquid ring vacuum pump (8B) and as motive fluid to liquid ejector (8A) through the circulation pump (13) and cooler (5). The intermittent cooler (5) takes care of the heat of reaction and compression. Eventually, the final traces of unreacted Ketene, which is released from the top of the packed column (2) through stream (10), is absorbed into the Ketene scrubber (11). Ketene is scrubbed with water entering through stream (12), to form weak acetic acid, which is removed through the bottom outlet (14).

EXAMPLES
Example 1:
Feed solution comprising of MDC as solvent having concentration of 51 % w/w MMP, was premixed with PTSA catalyst. Catalyst was added to the extent of 0.75% w/w of the MMP within the solution. Said pre- mixed feed solution was kept ready in the dosing tank, to be fed as ring liquid reactant at the rate of 350 lph to the liquid ejector (8A) and ring liquid vacuum pump system (8B). Liquid circulation loop was established by circulating the premixed feed solution through section in the sequence of packed column (2), liquid ejector (8A), liquid ring vacuum pump (8B), gas inducing reactor (8D) and back to the dosing tank.
With the aid of the vacuum, equimolar supply of Ketene gas was initiated into the system. Ketene of 95% purity is fed at the rate of around 70 kg/h. Injection of Ketene gas leads to the intimate contact between the two phases within the system, resulting into the progression of the acetylation reaction. Reaction being mildly exothermic, heat of the reaction is absorbed by bringing brine circulation cooler in loop. Reaction temperature of 25°C is maintained in the liquid ring vacuum pump (8B). Solution leaving the pump still has around 30% of unreacted MMP. Partially converted reactant solution is sent to gas inducing reactor (8D) for completing the balance reaction. Here, the reaction temperature is bit elevated to 35°C to ensure complete conversion of the MMP. Traces of unreacted Ketene gas is utilized by allowing it to react with fresh feed solution in the packed column (2). Complete system volume and the said feed rate results into the reaction residence time of 6 hrs. In this case, rate of MMP conversion is relatively better in initial period, however, as

reaction proceeds; feed solution starts becoming progressively viscous, thereby dropping conversion levels of MMP as well as Ketene gas. Acidity of weak acid indicates Ketene loss to the extent of 18.5%.
Product solution containing Acephate is collected in a separate tank, from where it is sent for further processing. MMP is reported of having been converted to the extent of 77.5%, with product selectivity of 95.3%, thus, resulting overall reaction yield of 73.8%. Unreacted Ketene gas is scrubbed with water to give acetic acid. Subsequent processing of the product mass after reaction, gives final product (Acephate) of purity 97%. Refer table no. 1 for more details.
Table 1

Feed Rate-MMP % Initial Cone, Of Reaction Residence Feed Rate-Ketene %MMP % Overall MMP % Ketene % Selectivity % Yield (w.r.t
Solution [Iph] MMP Solution Time [hrs] Gas [kg/hi Unreacted Conversion Lost (w.r.tMMP) MMP1 ■
0 51% 0 0 51 0.0 0.0 0.0 0
2100 51% 1 421 32 37.3 60.8 98.7 36.8
1050 51% 2 211 17 66.7 29.8 98.2 65.5
700 51% 3 140 14 72.5 23.6 97.4 70,7
525 51% 4 105 13 74.5 21.6 97.2 72,4
420 51% 5 84 13 75.1 20.9 96.8 72.7
350 51% 6 70 11,5 77.5 18.5 95.3 73.8
300 51% 7 60 11.3 77.8 18.1 93.2 72.5
263 51% 8 53 11.3 77.8 18.1' 91.4 71.1
Example 2:
Feed solution comprising of MDC as solvent having concentration of 25% w/w of MMP was premixed with PTSA catalyst. Catalyst was added to the extent of 1% (w/w) of the MMP within the solution. Said pre- mixed feed solution of reactant

and catalyst was kept ready in the dosing tank, to be fed as ring liquid reactant at the rate of 350 lph to the liquid ejector (8A) and ring liquid vacuum pump system (8B). Liquid circulation loop was established by circulating the premixed reactant solution through section in the sequence of packed column (2), liquid ejector (8A), liquid ring vacuum pump (8B), gas inducing reactor (8D) and back to the dosing tank.
With the aid of the vacuum, equimolar supply of Ketene gas into the system was initiated. Ketene of 95% purity is fed at the rate of around 47 kg/h. Injection of Ketene gas leads to the intimate contact between 2 phases within the system, resulting into the progression of the acetylation reaction. Reaction being mildly exothermic, heat of reaction is absorbed by bringing brine circulation cooler in loop. Reaction temperature of 20°C is maintained in the liquid ring vacuum pump (8B). Partially converted reactant solution is sent to gas inducing reactor (8D) for completing the balance reaction. Here, the reaction temperature is bit elevated to 30°C to ensure complete conversion of the MMP. Traces of unreacted Ketene gas is utilized by allowing it to react with fresh feed solution in the packed column (2). Complete system volume and the said feed rate results into the reaction residence time of 6 hrs. In this case, rate of MMP conversion is found to be low and almost steady throughout the reaction. However, acidity of weak acid doesn't reconcile with the unreacted Ketene going out from the system. This indicates involvement of Ketene gas into self reaction (dimerisation and tetramerisation) and formation of liquid impurities.
Product solution containing Acephate is collected in a separate tank, from where it is sent for further processing. MMP is reported of having been converted to the

extent of 84%, with product selectivity of 95.2%, thus, resulting overall reaction yield of 80%. Unreacted Ketene gas is scrubbed with water to give acetic acid. Subsequent processing of the product mass after reaction, gives final product (Acephate) of purity 96%. Refer table no. 2 for more details. Table 2

Feed Rate.MMP % Initial Conc Of Reaction Residence Feed Rate-Ketene 54 MMP % Overall MMP % Ketene % Selectivity % Yield [w.r.t
Solution [lph] MMP Solution Time [hrsj Sas [kg/h] Unreacted Conversion Lost (w.r.tMMP| MMP)
0 25% 0 0 25 0.0 0.0 0.0 0
2100 25% 268 20 20.0 83.8 98.0 19.6
1050 25% 138 17 32.0 74.9 97.3 31.1
700 25% 92 13 48.0 62.0 97.1 46.6
525 25% 67 9 64.0 48.2 96.7 61.9
420 25% 55 5 80.0 37.2 96.5 77.2
350 25% 6 47 4 84.0 35.9 95.2 80.0
300 25% 7 41 3 88.0 33.8 92.5 81.4
263 25% 8 37 2 92.0 33.2 90.2 83.0
Example 3:
Feed solution comprising of MDC as solvent having concentration of 35% w/w MMP was premixed with PTSA catalyst. Catalyst was added to the extent of 0.85% w/w of the MMP within the solution. Said pre- mixed feed solution was kept ready in the dosing tank, to be fed as ring liquid reactant at the rate of 350 lph to the liquid ejector (8A) and ring liquid vacuum pump system (8B). Liquid circulation loop was established by circulating the premixed reactant solution through section in the sequence of packed column (2), liquid ejector (8A), liquid ring vacuum pump (8B), gas inducing reactor (8D) and back to the dosing tank.
With the aid of the vacuum, equimolar supply of Ketene gas into the system was initiated. Ketene of 95% purity is fed at the rate of around 48 kg/h. Injection of Ketene gas leads to the intimate contact between 2 phases within the system,

resulting into the progression of the acetylation reaction. Reaction being mildly exothermic, heat of reaction is absorbed by bringing brine circulation cooler in loop. Reaction temperature of 25°C is maintained in the liquid ring vacuum pump (8B). Partially converted reactant solution is sent to gas inducing reactor for completing the balance reaction. Here, the reaction temperature is bit elevated to 35°C to ensure complete conversion of the MMP. Traces of unreacted Ketene gas is utilized by allowing it to react with fresh feed solution in the packed column (2). Complete system volume and the said feed rate results into the reaction residence time of 6 hrs. In this case, rate of MMP conversion is found to be steadily increasing throughout the reaction. Unreacted Ketene gas is scrubbed with water to give acetic acid.
Product solution containing Acephate is collected in a separate tank, from where it is sent for further processing. MMP is reported of having been converted to the extent of 99.2%, with product selectivity of 98%, thus, resulting overall reaction yield of 97.2%. Subsequent processing of the product mass after reaction, gives final product (Acephate) of purity 97.5%. Refer table no. 3 for more details.
Table 3

Feed Rate -MMP % Initial Conc. Of Reaction Residence Feed Rate -Ketene %MMP % Overall MMP % Ketene % Selectivity % Yield (w.r.t
Solution Pph] MMP Solution Time [hrs] Gas[kg/h] Unreacted Conversion lost |w.r.t MMP) MMP)
0 35% 0 0 35 0.0 0.0 0.0 0
2100 35% 1 289 25 28.6 69.9 99.5 Z8.4
1050 35% 2 144 15 57.1 39.8 99.1 56.6
700 35% 3 96 9 74.3 21.8 98.9 73.5
525 35% 4 72 4 88.6 6.8 98.8 87.5
420 35% 5 58 2 94.3 1.2 ' 98.5 92.9
350 35% 6 48 0.28 99.2 1.0 98.0 97.2
300 35% 7 41 0.22 99.4 1.0 97.3 96.7
263 35% 8 36 0.15 99.6 1.0 95.2 94.8

Example 4:
Feed solution comprising of MDC as solvent having concentration of 30% w/w MMP was premixed with PTSA catalyst. Catalyst was added to the extent of 0.9% w/w of the MMP within the solution. Said pre- mixed feed solution was kept ready in the dosing tank, to be fed as ring liquid reactant at the rate of 420 lph to the liquid ejector (8A) and ring liquid vacuum pump system (8B). Liquid circulation loop was established by circulating the premixed reactant solution through section in the sequence of packed column (2), liquid ejector (8A). liquid ring vacuum pump (8B), gas inducing reactor (8D) and back to the dosing tank.
With the aid of the vacuum, equimolar supply of Ketene gas into the system was initiated. Ketene of 95% purity is fed at the rate of around 66 kg/h. Injection of Ketene gas leads to the intimate contact between 2 phases within the system, resulting into the progression of the acetylation reaction. Reaction being mildly exothermic, heat of reaction is absorbed by bringing brine circulation cooler in loop. Reaction temperature of 30°C is maintained in the liquid ring vacuum pump (8B). Partially converted reactant solution is sent to gas inducing reactor for completing the balance reaction. Here, the reaction temperature is bit elevated to 35°C to ensure complete conversion of the MMP. Traces of unreacted Ketene gas is utilized by allowing it to react with fresh feed solution in the packed column (2). Complete system volume and the said feed rate results into the reaction residence time of 5 hrs. In this case, rate of MMP conversion is found to be steadily increasing throughout the reaction. Unreacted Ketene gas is scrubbed with water to give acetic acid.

Product solution containing Acephate is collected in a separate tank, from where it is sent for farther processing. MMP is reported of having been converted to the extent of 98.4%, with product selectivity of 98.2%, thus, resulting overall reaction yield of 96.6%. Subsequent processing of the product mass after reaction, gives final product (Acephate) of purity 97.0%. Refer table no. 4 for more details.
Table 4

Feed Rate-MMP % Initial Cone, Of Reaction Residence Feed Rate -Ketene %MMP % Overall MMP %• Ketene % Selectivity % field (w.r.t
Solution [Iph] MMP Solution Time [hfs| Gas [kg/h] threaded Conversion Lost (w.r.t. MMP) MMP)
0 30% 0 0 30 0.0 0.0 0.0 0
2100 30% 1 322 19 24.0 80.6 99.5 23.9
1050 30% 2 166 12 52.0 55.0 98.6 51.3
700 30% 3 110 5 80.0 19.0 98.2 78.6
525 30% 4 81 2 92.0 5.0 98.6 90.7
420 30% 5 66 0.40 98.4 1.0 98.2 96.6
350 30% 6 57 0.35 98.6 1.0 96i 95.1
300 30% 7 50 0.30 98.8 1.0 94.0 92.9
263 30% 8 45 0.20 99.2 0.5 89.0 88.3

We claim;
1. A method for continuous manufacturing of Acephate comprising of acetylation of O-S-Dimethyl Thiophosphamaide (Methamidophos/MMP) by absorption of Ketene under vacuum in presence of p-Toluenesulphonic acid (PTSA) as catalyst and Methylene dichloride (MDC) as solvent.
2. A method as claimed in Claim 1 wherein the reaction temperature varies between 15°C and 35°C and the reaction time varies between 6 and 8 hours.
3. A method as claimed in Claim 1 wherein concentration of MMP in solvent MDC is between 25% and 51 %.
4. A method as claimed in Claim 1 wherein Ketene and the liquid reaction mixture comprising said MMP, MDC and PTSA flow co-currently or counter-currently or in combination of both.
5. A method as claimed in Claim 1, wherein isolation of pure Acephate is obtained by solvent concentration, crystallization, solid-liquid separation and drying.
6. A method as claimed in Claim 5 wherein resultant mother liquor obtained after isolation of Acephate is recycled in subsequent batches.
7. An apparatus for continuous production of Acephate comprising two or more reaction vessels connected in series or parallel, each having a device to create

vacuum; inlets to receive unreacted or partly reacted mixture of MMP, MDC and PTSA and Ketene; and an outlet.
8. An apparatus as chimed in Claim 7 wherein the inlets of liquid reaction mixture comprising said MMP, MDC and PTSA and Ketene in a reaction vessel are positioned so as to flow said liquid reaction mixture and Ketene co-currently or counter-currently.
9. An apparatus as claimed in Claim 7 wherein a gas liquid separator is connected to the outlet of the last reaction vessel in series or to each of the reaction vessels in parallel.
10. An apparatus as claimed in Claim 7 wherein the device to create vacuum is a liquid ring vacuum pump.
11. An apparatus as claimed in Claim 7 wherein the device to create vacuum is a gas inducing impeller and wherein a gas liquid separator is provided before the reaction vessel having the said gas inducing impeller.
12. An apparatus as claimed in Claim 7 wherein the reaction vessels are in series and in the first reaction vessel the device to create vacuum is liquid ejector followed by reaction vessels having liquid Ting vacuum pump and/or gas inducing impeller.