FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
AND
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
"AN IMPROVED DRYING PROCESS"
We, UNITED PHOSPHORUS LIMITED,
Uniphos House,
11th Road, C. D Marg, Khar (West),
Mumbai-400 052,
State of Maharashtra
INDIAN.
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:-

The present invention relates to a process for the preparation of Mancozeb powder having low moisture content. The present invention particularly relates to an improved low cost process for drying Mancozeb slurry under controlled vacuum for the preparation of Mancozeb powder having low moisture content.
Background and Prior art:
Mancozeb (MNZ) [Formula (I)] is a fungicide comprising mainly a co-ordination product of Zinc and Manganese alkylene (usually ethylene) bis dithiocarbamate. It is commercially available in dust, powder, or granular form. It is unstable and prone to degradation by oxidation and moisture. The conventional processes for the preparation of mancozeb afford a slurry having a moisture content of about 55%. It is then further dried to a powder form. It has been observed that during this drying stage, any contact with air leads to deterioration of the ethylene dithiocarbamate to ethylenethiourea (ETU), which reduces its fungicidal activity. Moreover, in the said drying stage, carbon disulphide is also formed as a decomposition by-product of Mancozeb, which imparts a foul odour to the final product. The by-product carbon disulphide and other generated carcinogenic sulphur compounds also cause environmental pollution problems. Moreover, drying mancozeb slurry to mancozeb powder having desired level of moisture content in the presence of moisture causes serious fire hazards. In order to reduce the degradation of ethylene dithiocarbamate to ETU to retard the degradation of mancozeb producing, inter alia, carbon disulfide, addition of stabilizing agents is recommended in the art. These known stabilizing agents, when added to mancozeb powder, increase the stability of Mancozeb powder.


(I) Mancozeb
Conventionally the mancozeb slurry having a moisture content of about 55% is dried in rotary vacuum driers (RVD). However, this method is .inefficient and extremely time-consuming because of indirect heating, which reduces convection heat transfer. Further, drying in RVD does not help reducing moisture to less than 3%-5% by weight which still renders the mancozeb powder unstable. It has been found that dried mancozeb powder having moisture content in the range of from about 3% to about 5% still remains susceptible to degradation on storage. It is therefore desirable to prepare dried mancozeb powder having moisture content less than the hitherto known range of from about 3% to about 5% by weight.
CN1040583 discloses preparation of mancozeb by complexing Maneb with Zinc sulphate in an organic solvent with dehydration and conversion into crystals simultaneously. This publication recommends the use of a membrane type evaporator or jet spray drying instead of the conventional rotary vacuum drying (RVD) as it is inefficient. This publication also teaches the use of an organic solvent, which acts as a moisture carrier and also helps in removing water by azeotrophic distillation. However, separation of the organic solvent from the final mancozeb product is an additional step required in the process disclosed herein, which adds cost and increases the process-time required to obtain the dried mancozeb powder having a desired moisture content.
CN1334006 discloses a vacuum drying process which is slow, labour intensive and batch type process, which affords an unstable product and also involves frequent fire hazards. The disclosed vacuum drying process is thus replaced by a spray drying process, which is carried out in a gas drying tower. However, the disclosed spray drying process involves beating and grinding mancozeb into 10%-50% concentrated pulp having a particle size less than 2.5 urn to obtain water dispersible mancozeb powder. The drying gas mixture flow temperature is from 100 C-300 C. It has two cyclonic separators in series operating at about 80°C. However, the disclosed spray drying process is not only slow but also time consuming and the drying temperatures are as high as 100°C-300 °C, which again leads to degradation of mancozeb. apart from posing significant fire hazards.

CN1975303 discloses a closed loop circulating drying method and a device comprising a drier, a cyclone separator, an after-heat recoverer device, a blower, a spray tower, a heater, and a dry-product cooler. The disclosed method comprises exchanging heat between mancozeb and nitrogen or carbon dioxide in the drier at 140-25 0°C. The dry product is collected with the help of cyclone separator and bag-type duster and then cooled at room temp. The method is highly efficient with low energy consumption and high safety.
Spray dried mancozeb slurry having up to 10-12 % by moisture weight is generally known in the art and found to be less susceptible to fire hazards but increasingly susceptible to degradation on storage. However spray drying mancozeb in conventional rotary vacuum dryers to reduce the moisture content to less than 5% by weight is hazardous.
In another process that is conventionally known in the art, mancozeb slurry is dried at a pressure ranging from about 0.99 torr (755 mm Hg) to around 5 torr, preferably at a temperature of around or greater than 100°C. It was observed by the present inventors that at a pressure of around 5 torr at the applied temperature of about 100 C Mancozeb degrades extensively.
Thus, it was concluded that the processes described in the prior art were not satisfactory and there existed a need to improve the known drying method to a preferably continuous process which was capable of affording dried mancozeb powder with much lower moisture content. It was further desirable that such improved process be not only more economical, less time and energy consuming but also that the end product should have excellent reproducibility and consistency of quality.
Objects of the Invention
Thus, one of the objects of the present invention is to provide a continuous process for drying mancozeb slurry.

Another object of the invention is to provide a continuous vacuum paddle drying process for drying Mancozeb slurry having initial moisture content in the range of 10% - 55% by weight to a dry powder having moisture content reduced to preferably less than 1% by weight.
Yet another object of the present invention is to provide an efficient low cost mancozeb drying process that reduces the fire hazards associated with the conventional processes involving direct heating.
Another object of the present invention is to provide a mancozeb slurry drying process which causes minimal deterioration of the final product.
Yet another object of the present invention is to provide a mancozeb slurry drying process having significant economic advantage over conventional processes.
Yet another object of the invention is to provide a process for drying mancozeb slurry that enables faster drying and more efficient heat recovery.
Another object of the present invention is to provide a process for drying mancozeb slurry which reduces the degradation of mancozeb during drying.
Yet another object of the present invention is to provide a process for drying mancozeb slurry which is capable of producing mancozeb powder having high purity.
Another object of the present invention is to provide a closed system for drying mancozeb slurry which reduces the explosion and fire hazards observed with the conventional drying systems.
These and the other objects and advantages of the present invention will be evident from the description of the invention following hereinafter.

Summary of the invention
A continuous process for drying a wet mass of mancozeb slurry to obtain dried mancozeb comprising continuously drying a mancozeb slurry having a predetermined moisture content in a provided paddle dryer for at least about 20 minutes at a controlled vacuum of from about 500mm Hg column to about 700 mm Hg column at a temperature of from about 80°C to about 120°C.
In another aspect, the present invention provides a system for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1%, said system comprising:
(a) an inlet capable of feeding a provided wet mass of mancozeb slurry having predetermined moisture content to a provided continuous paddle dryer;
(b) a continuous paddle dryer comprising a jacket which has temperature maintained from about 80°C to about 120°C and a plurality of substantially hollow paddles mounted onto a motor driven central shaft and adapted to rotate at a controlled speed of rotation; and
(c) a paddle cooler comprising a cooling jacket and a plurality of hollow paddles mounted
on a motor driven central shaft, said paddle cooler comprising an inlet means connected
to the paddle dryer outlet and capable of receiving the hot dried mancozeb powder and
carrying the received hot dried mancozeb powder within the paddle cooler, said paddle
cooler further comprising a coolant circulation means comprised within said paddle
cooler which is capable of circulating a chilled fluid throughout the paddle cooler, said
paddle dryer being maintained at a controlled vacuum of from about 500 mm Hg to about
700 mm Hg;
In another aspect, the present invention provides a system for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1%, said system comprising:
(a) an inlet capable of feeding a provided wet mass of mancozeb slurry having predetermined moisture content to a provided continuous paddle dryer;

(b) a continuous paddle dryer comprising a jacket which has temperature maintained from about 80°C to about 120°C using pressurized steam at a pressure of from about 0.8 kg/cm2 to about 1.5 kg/cm2, said continuous paddle dryer additionally comprising a plurality of substantially hollow paddles mounted onto a motor driven central shaft and adapted to rotate at a controlled speed of rotation;
(c) a paddle dryer outlet capable of receiving the hot dried mancozeb powder from the paddle dryer and feeding said hot dried mancozeb powder to a provided paddle cooler;
(d) a paddle cooler comprising a cooling jacket and a plurality of hollow paddles mounted on a motor driven central shaft, said paddle cooler comprising an inlet means connected to the paddle dryer outlet and capable of receiving the hot dried mancozeb powder and carrying the received hot dried mancozeb powder within the paddle cooler, said paddle cooler further comprising a coolant circulation means comprised within said paddle cooler which is capable of circulating a chilled fluid throughout the paddle cooler, said paddle dryer being maintained at a controlled vacuum of from about 500 mm Hg to about 700 mm Hg;
(e) a fines separator comprising a cyclone and a bag filter having sufficiently high surface area capable of collecting fine particles of mancozeb and conveying said collected fine particles to a chilled water scrubber;
(f) a chilled water scrubber for collecting fine particles of mancozeb and contacting said collected particles to the chilled fluid being circulated through the paddle cooler and thereafter conveying the collected fine cooled mancozeb particles to be recycled into the drying system; and
(g) a paddle cooler outlet capable of conveying the remaining dried and cooled mancozeb powder out of said drying system to a plurality of external packaging locations.
Detail description of a preferred embodiment of the present invention
The present invention is thus based on the surprising finding that the degradation of mancozeb product obtained by paddle drying a wet mass of mancozeb slurry is surprisingly reduced when said drying process is carried out at a reduced pressure of about 500-700 torr at a temperature ranging from about 80°C -120°C even though the known processes at 100°C caused extensive degradation of the mancozeb product.

Accordingly, in one aspect, the present invention provides a continuous process for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1%, said process comprising continuously drying mancozeb slurry in a provided paddle dryer for at least about 20 minutes at a controlled vacuum of from about 500mm Hg column to about 700 mm Hg column at a temperature of from about 80°C to about 120°C. ( Refer Table 2, 3 and 4).
In an embodiment of this aspect of the invention, said mancozeb slurry having a predetermined moisture content that is continuously dried in the provided paddle dryer has a moisture content of from about 10% to about 12% by weight and is obtained by a first drying step which comprises either spray drying an initial slurry or drying the initial slurry in a rotary vacuum dryer.
In an embodiment, the first drying step comprises spray drying an initially provided wet mass of mancozeb slurry having moisture content from about 10% to about 55% to obtain a second mancozeb slurry having moisture content from about 10% to about 12% by
weight.
Accordingly, in one aspect, the present invention provides a continuous process for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1%, said process comprising:
(a) spray drying an initially provided wet mass of mancozeb slurry having moisture content from about }Q% to about 55% to obtain a second mancozeb slurry having a moisture content from about 10% to about 12%;
(b) continuously drying said second mancozeb slurry in a provided paddle dryer for at least about 20 minutes at a controlled vacuum of from about 500mm Hg column to about 700 mm Hg column at a temperature of from about 80°C to about 120°C.
In another aspect, the present invention provides a continuous process for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1 %, said process comprising:

(a) drying an initially provided wet mass of mancozeb slurry having moisture content from about 10% to about 55% in a rotary vacuum dryer to obtain a second mancozeb slurry having a moisture content from about 10% to about 12%; and
(b) continuously drying said second mancozeb slurry in a provided paddle dryer for at least about 20 minutes at a controlled vacuum of from about 500 ton to about 700 torr at a temperature of from about 80°C to about 120°C.
In another aspect, the present invention provides a system for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1%, said system comprising:
(a) an inlet capable of feeding a provided wet mass of mancozeb slurry having predetermined moisture content to a provided continuous paddle dryer;
(b) a continuous paddle dryer comprising a jacket which has temperature maintained from about 80°C to about 120°C using pressurized steam at a pressure of from about 0.8 kg/cm2 to about 1.5 kg/cm2, said continuous paddle dryer additionally comprising a plurality of substantially hollow paddles mounted onto a motor driven central shaft and adapted to rotate at a controlled speed of rotation; and
(c) a paddle cooler comprising a cooling jacket and a plurality of hollow paddles mounted
on a motor driven central shaft, said paddle cooler comprising an inlet means connected
to the paddle dryer outlet and capable of receiving the hot dried mancozeb powder and
carrying the received hot dried mancozeb powder within the paddle cooler, said paddle
cooler further comprising a coolant circulation means comprised within said paddle
cooler which is capable of circulating a chilled fluid throughout the paddle cooler; and
wherein said paddle dryer is maintained at a controlled vacuum of from about 500 mm Hg to about 700 mm Hg.
In an embodiment, said paddle dryer comprises a paddle dryer outlet which receives the hot dried mancozeb powder from the paddle dryer and feeds the received hot and dried mancozeb powder to a provided paddle cooler.

In another embodiment, the paddle cooler includes at least one paddle cooler outlet which conveys the remaining dried and cooled mancozeb powder out of the drying system to a plurality of external packaging locations.
Preferably, the system according to the present invention is capable of separating coarse dried mancozeb particles from fine particles. In this embodiment, the system of the present invention comprises a fines separator comprising a cyclone and a bag filter having sufficiently high surface area capable of collecting fine particles of mancozeb and conveying the collected fine particles to a chilled fluid scrubber, preferably a chilled water scrubber.
The provided chilled water scrubber collects fine particles of mancozeb and contacts the collected particles to the chilled fluid being circulated through the paddle cooler. The chilled fluid scrubber thereafter conveys the collected fine cooled mancozeb particles to the recycling means which recycles the fine particles into the drying system of the present invention.
Accordingly, in another embodiment, the present invention provides a system for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1%, said system comprising:
(a) an inlet capable of feeding a provided wet mass of mancozeb slurry having predetermined moisture content to a provided continuous paddle dryer;
(b) a continuous paddle dryer comprising a jacket which has temperature maintained from about 80°C to about 120°C using pressurized steam at a pressure of from about 0.8 kg/cm2 to about 1.5 kg/cm2, said continuous paddle dryer additionally comprising a plurality of substantially hollow paddles mounted onto a motor driven central shaft and adapted to rotate at a controlled speed of rotation;
(c) a paddle dryer outlet capable of receiving the hot dried mancozeb powder from the paddle dryer and feeding said hot dried mancozeb powder to a provided paddle cooler;
(d) a paddle cooler comprising a cooling jacket and a plurality of hollow paddles mounted on a motor driven central shaft, said paddle cooler comprising an inlet means

connected to the paddle dryer outlet and capable of receiving the hot dried mancozeb powder and carrying the received hot dried mancozeb powder within the paddle cooler, said paddle cooler further comprising a coolant circulation means comprised within said paddle cooler which is capable of circulating a chilled fluid throughout the paddle cooler, said paddle dryer being maintained at a controlled vacuum of from about 500 mm Hg to about 700 mm Hg;
(e) a fines separator comprising a cyclone and a bag filter having sufficiently high surface area capable of collecting fine particles of mancozeb and conveying said collected fine particles to a chilled water scrubber;
(f) a chilled water scrubber for collecting fine particles of mancozeb and contacting said collected particles to the chilled fluid being circulated through the paddle cooler and thereafter conveying the collected fine cooled mancozeb particles to be recycled into the drying system; and
(g) a paddle cooler outlet capable of conveying the remaining dried and cooled mancozeb powder out of said drying system to a plurality of external packaging locations.
Accordingly, the present invention describes an improved low cost drying system for drying of Mancozeb slurry with reduced degradation, comprising conductive heating of the slurry in a continuous process wherein the plant comprises an enclosed paddle dryer and paddle cooler operating under controlled vacuum. The controlled vacuum transports the vapors emerging in the drying process within the heated dryer through the fines separating cyclones and filters and thereafter releases the vapors into a chilled water scrubber. A mancozeb slurry being continuously fed to the paddle dryer is dried and cooled in the provided paddle cooler and emerges as a dry free flowing powder for bulk packing.
In an embodiment, the controlled vacuum includes a low pressure atmosphere of nitrogen gas maintained throughout the paddle dryer and paddle cooler. Preferably, the low pressure nitrogen means nitrogen at a pressure of about 500 mm to about 700 mm of Hg column.

The process of the present invention is thus a continuous drying process using paddle dryer fitted with a jacket heated to a temperature 80-120 degrees. In a preferred embodiment, the jacket is heated using pressurized steam at a pressure of from about 0.8 kg/cm2 to about 1.5 kg/cm2. The paddle dryer additionally comprises a plurality of paddles mounted on a central shaft which is capable of being rotated at a controlled speed of rotation. The mancozeb slurry being dried is treated in the paddle dryer for at least about 20 minutes. It was found that greater lengths of time did not substantially effect the percentage purity of the final mancozeb product nor did it effect the moisture content substantially though time periods greater than about 60 minutes consumed greater power without offering any substantial benefit in terms of the purity or the moisture content of the final product. Thus, a time period of at least about 20 minutes, preferably from about 20 minutes to about 60 minutes was considered selective.
In another embodiment, the drying process is carried out at a controlled vacuum of about 500-700 mm Hg column.
The continuous process according to the present invention comprises feeding hot mancozeb slurry under controlled vacuum in the paddle dryer chamber. The fed mancozeb slurry churns and moves in the paddle dryer and continuously moves out as a hot dry powder into a continuous paddle cooler.
The process according to the present invention is found to possess high thermal efficiency. It enables drying at comparatively low temperature, to yield mancozeb powder of better quality with low impurities due to low degradation, which is believed to arise in part, due to the low heating time of at least about 20 minutes at a reduced temperature enabled in the process according to the present invention.
In an embodiment, the vacuum paddle dryer according to the present invention additionally comprises at least a product filter, a condenser, a receiver and at least one vacuum pump which is capable of mamtaining a controlled vacuum of from about 500 mm Hg to about 700 mm Hg.

It was found that the process described according to the present invention is highly cost effective with minimal degradation of the product. Without wishing to be bound by theory, it is believed that due to a controlled vacuum applied inside the paddle dryer, the boiling point of the solvent employed is reduced and as a result, the fed mancozeb slurry was dried at a much lower temperature than that enabled by the known processes. It was further found that due to low temperature employed in the process according to the present invention, the degradation of mancozeb powder is surprisingly low thereby also significantly reducing the associated fire hazard.
The present invention thus provides a process for drying mancozeb powder involving the use of a paddle dryer followed by a paddle cooler, both being enclosed and operating under controlled vaccum of 500-700 torr. It has been observed that a continuous operation of paddle dryer and paddle cooler under controlled vacuum conditions of the present invention was found to accelerate the water vapor evaporation at relatively low temperature. The controlled vacuum conditions employed in the present invention eliminates fire hazards observed in the conventional processes.
In a further preferred embodiment, the present invention thus provides a process for drying a wet mass of mancozeb slurry to mancozeb powder having moisture content less than 1% by weight, said process comprising:
(a) feeding a provided wet mass of mancozeb slurry having predetermined moisture content to a provided continuous paddle dryer within a provided drying system;
(b) drying said fed mancozeb slurry in said provided continuous paddle dryer at a temperature of from about 80 C to about 120 C;
(c) conveying hot dried mancozeb powder from said continuous paddle dryer and feeding said hot dried mancozeb powder to a provided paddle cooler;
(d) circulating a coolant fluid within said paddle cooler thereby cooling said fed hot dried mancozeb powder within the paddle cooler at a controlled vacuum of from about 500 mm Hg to about 700 mm Hg;
(e) separating and collecting fine particles of dried mancozeb in a provided fines separator and conveying the collected particles to a provided fluid scrubber;

(f) contacting said collected fine particles of mancozeb particles to a cooling fluid within said fluid scrubber;
(g) optionally recycling said cooled fine mancozeb powder particles into a provided drying system; and
(h) conveying the remaining dried and cooled mancozeb powder out of said drying system to a plurality of external packaging locations.
.The paddle dryer is a horizontal jacketed conveyor type of dryer with gas tight enclosure having twin hollow rotor shafts driven by motors and is fitted with hollow paddles for steam heating. In an embodiment of the present invention, a preferred temperature of about 80 C to about 120 C using pressurized steam at a pressure of about 0.8 to about 1.5 kg/cm2. The paddle dryer further comprises an inlet for feeding moist mancozeb powder and an outlet for conveying the hot dry powder to a connected feeding hopper of the paddle cooler through air tight rotary valves.
In another embodiment, the paddle dryer further comprises an outlet means for carrying any moisture generated during drying of said moist mancozeb powder and releasing the same to the external environment.
The starting mancozeb slurry of the present invention has initial water content of from about 10% to about 55% by weight as formed in the reaction vessel during the chemical preparation of mancozeb. The preferred mancozeb slurry which is suitable as a starting material for the process according to the present invention has a moisture content of from about 10 to about 12% by weight, which is generally obtained by initial spray drying of the Mancozeb formed in the reaction vessel in its preparation.
The paddle cooler comprises a single hollow shaft rotor with hollow paddles rotated by a motor, an inlet for hot dried Mancozeb powder coming out of the outlet of the paddle drier, with chilled water circulating in the shaft and the paddles and an outlet for taking the cooled powder out to the packaging containers under controlled vacuum of 500-700 torr.

The continuous paddle dryer suitable for the present invention has a jacket and hollow paddles for steam heating. It is air tight closed to maintain a controlled vacuum inside. It has airtight opening for mancozeb input feed and another airtight opening for output discharge. It has steam inlet and condensate outlet. In the paddle dryer there are two hollow shafts (rotors) carrying intermeshed paddles and a motor drive for double shaft agitator.
The provided continuous paddle cooler has a jacket and hollow paddles for cooling the hot dry powder coming out of outlet of the paddle dryer and coming into the paddle cooler through its inlet, with chilled water circulation in the jacket and the paddles and a single paddle shaft rotated by a motor. It has one inlet and one outlet or a continuous feeding output of the paddle dryer and taking it out after cooling, to the packaging machine. Both the inlet and outlets are fitted with rotary valves to keep the mass flowing continuously, without exposure to the air.
In another embodiment, the system of the present invention comprises a cyclone for settling fines and a plurality of filter bags to collect fines escaping the cyclone arrangement. A chilled water scrubber is provided wherein very fine particles escaping filter bags are brought in contact with chilled water from chilled water cooler circulated by pumps. The sequential arrangement of cyclone, fines separator, filter bags, contact collector and water scrubber ensures that no mancozeb fines escape to the atmosphere. The chilled water used for scrubbing is passed out through the effluent treatment plant.
In an optional embodiment, fresh compressed nitrogen is also fed in to the bag filters for removing fines. In another preferred embodiment, the pulsation of a provided contact collector is used for back-flushing of the filter bags.
The starting material is obtained by drying of Mancozeb slurry having initial moisture content around 50% by weight, in a spray dryer or in a rotary vacuum dryer, which operates in a continuous mode. The spray dryer uses hot air at about 250C - 300 °C. The Mancozeb gets dried up to a moisture content of only about 10-12 % by weight, in the
spray dryer.

In an embodiment, mancozeb slurry having moisture content about 10-12 % by weight is used as a starting material to be fed in the vacuum paddle dryer.
In another embodiment, mancozeb slurry with moisture content about 55% by wt. obtained from the Mancozeb reaction vessel or with about 10-12 % moisture obtained from spray dryer held in a silo, is continuously fed to continuous paddle dryer through rotary valve; (ii) the exiting hot dry Mancozeb powder is fed to paddle cooler; (iii) the cooled product is preferably packed under nitrogen atmosphere; (iv) the cooled fines collected in the cyclone are pushed back to the main chamber and packed under nitrogen atmosphere; (viii) the temperature of chilled water in contact condenser is maintained to a desired level. In this embodiment, steam at a pressure of about 0.8-1.5 Kg/cm2 is used as a preferable medium for heating and drying of the Mancozeb powder preferably at 80°C-120°C.
In a preferred embodiment, the paddle dryer is preferably fabricated from stainless steel (SS316) which has a high heat transfer coefficient. The hollow rotating shafts and connected hollow paddles have means to connect them to the steam supply and condensed water exhaust traps outside the paddle dryer. The arrangement of the paddles on the twin shafts rotating in opposite directions at a slow speed of about 10-30 rpm preferably at 15 - 25 rpm, are driven by a motor outside the dryer.
The final dried mancozeb powder, which emerges out of the system according to the present invention, has a temperature of about 20 C - 40 C preferably at about 25°C - 35°C, is then packed under nitrogen, in bulk in bags or in any suitable containers. The process of the present invention is significantly economically advantageous. It has been observed that the cost of drying in the process of the present invention is surprisingly reduced in comparison to the drying cost in the rotary vacuum drying process conventionally known in the art.
The product obtained in the examples described hereinafter demonstrate that the quality of mancozeb powder prepared according to the process of the present invention meets the

in-house specifications and is superior in having fewer impurities than that the product prepared by the conventionally known processes.
The invention will now be illustrated with the help of examples, which are provided for mere illustration and are not to be construed as limiting the scope of the invention in any manner.
Example I
Drying Mancozeb slurry from 11 % by wt to Mancozeb powder having less than 1 % by wt of moisture using Vacuum paddle dryer.
The starting Mancozeb used in this example was obtained from drying slurry of the composition in a spray tower with using hot air bringing down the moisture from about 55 % by wt. to about 10% by wt.
The present example describes a plant for drying of mancozeb comprising a continuous paddle dryer working with paddles on two shafts rotating in same or counter directions. The paddle dryer was operated under a controlled vacuum, which carried the vapors generated from evaporation of the moisture present in the fed mancozeb and deposited it in chilled water in a direct contact scrubber.
The spray dryer output of Mancozeb with about 10% moisture by weight was fed into the paddle dryer. The paddle dryer was heated with steam at a pressure of about 0.8 to about 1.5 kg/cm2 at steam inlet and condensate outlet: The shafts rotated at about 20 rpm. The output was fed to the paddle cooler. The dried product emerged from the paddle dryer and was fed to the paddle cooler inlet and subsequently, upon cooling, emerged through the cooler outlet in to the bulk packs.
In this exemplary embodiment, dried mancozeb powder was obtained at 80 C having about 0.78 % by weight moisture content. The fines were recovered from the cyclone and filter bags. The equipment was operated for about 35 minutes.

For the purpose of comparison of costs for the drying system of the present invention as described in example I, mancozeb slurry of similar moisture was dried to dry powder of similar moisture levels as in example II.
Example II.
This is a comparative example of the conventional rotary vacuum dryer process which is not part of this invention.
A mancozeb slurry having 11.57% moisture was charged to a rotary vacuum dryer. The final moisture content in this process was 5.09%. The heating time required in this process was almost for 35 mins.
The properties of the product obtained in Example 1 and Example 2 are compared in Table 1.
TABLE 1:
% puritv of Mancozeb content when used different dryers

The above table illustrated that when the temperature, pressure and time were kept same using two different dryers namely vacuum paddle dryer and rotary vacuum dryer, it was surprisingly observed that the mancozeb degradation was less when vacuum paddle dryer was used instead of the conventionally used rotary vacuum dryer.

It was thus surprisingly found that mancozeb degradation was least when vacuum paddle dryer was operated in a continuous process for a time period of at least about 20 minutes, more preferably from about 20 minutes to about 60 minutes at a controlled vacuum of from about 500mm Hg column to about 700 mm Hg column at a temperature of from about 80°C to about 120°C. It was found that greater lengths of time did not substantially effect the percentage purity of the final mancozeb product nor did it effect the moisture content substantially though time periods greater than about 60 minutes consumed greater power without offering any substantial benefit in terms of the purity or the moisture content of the final product. Thus, a time period of at least about 20 minutes, preferably from about 20 minutes to about 60 minutes was considered selective.

The above table 4 demonstrates that when vacuum paddle dryer and Rotary vacuum dryer both operated from about 500mm Hg column to about 700 mm Hg column at a temperature ranging from about 80°C to about 120°C, it has been observed that vacuum paddle dryer results into less mancozeb degradation compared to rotary vacuum dryer.
TABLE 5:
Long term stability for at least 3 batches of Mancozeb dried using Vacuum paddle dryer are tested and the stability of the product is monitored for 21 days at 54±2°C


All the three batches of Mancozeb that are dried using vacuum paddle dryer and tested for long term stability are found stable till its shelf life.
TABLE 6:
Three batches are subjected to drying at 80°C, for 30 minutes using vacuum paddle dryer Vs Rotary Vacuum dryer. The vacuum maintained in Vacuum paddle dryer is 500-700 torr.

It was observed that mancozeb powder prepared by the process according to the present invention demonstrates less LOD as compared to LOD offered by rotary vacuum dryer.
Cost comparison of Example I and that of Example II shows that the cost of drying in the system of the present invention is significantly reduced to less than half the cost of drying in Rotary vacuum dryer.
The table 7 appearing below demonstrates the details for the drying cost per Kg. of dried mancozeb in vacuum paddle dryer (according to the present invention) and the drying cost of mancozeb per Kg using rotary vacuum dryer under identical conditions.
TABLE 7


Thus one or more surprising advantages of the invention was that the mancozeb wet mass was safely dried to moisture content of less than 1% in less than 30 minutes to reduce the fire hazard and instability of mancozeb. It was further found that the process of drying mancozeb was economically cheaper and it cost less than half the cost of drying according to the conventional process. It was found that the drying time was drastically reduced in comparison to the conventional processes and the moisture content is lowered to below 1% by weight. It was also found that the process of the present invention consumed less energy.
Another advantage of the process and system according to the present invention is that it could be used for drying of other alkylenebisdithiocrbamates like Maneb, Zineb.
It was further found that the quality such as percentage purity and/or moisture content of the product according to the present invention was superior to that obtained by the conventional process of rotary vacuum drying. It is believed that due to the controlled vacuum applied, the boiling point of the solvent is reduced and the rate of evaporation is increased.
The process of the present invention enabled reduction of the obnoxious odor of mancozeb powder by reducing the degradation of the final product, thus leading to a more consumer acceptable product. Further, the drying or residence time of mancozeb was reduced to a considerable extent without compromising the product quality. Moreover, the drying process described in this invention was continuous and closed operation, such that an accidental entry of any foreign material in the final product was less likely in the present process.
Although the invention has now been described with reference to specific preferred embodiments, it is not intended to be limited thereto but rather those skilled in the art will recognize that the variations and modifications may be made therein which are within the spirit of the invention and within the scope of the present description.

We Claim:
1. A continuous process for drying a wet mass of inancozeb slurry to obtain dried mancozeb, said process comprising continuously drying a mancozeb slurry having a predetermined moisture content in a provided paddle dryer for at least about 20 minutes at a controlled vacuum of from about 500mm Hg column to about 700 mm Hg column at a temperature of from about 80 C to about 120°C.
2. The process as claimed in claim 1, wherein said dried mancozeb has a moisture content of less than about 1 %.
3. The process as claimed in claim 1 or claim 2, wherein said mancozeb slurry has a moisture content of from about 10% to about 12% by weight.
4. The process as claimed in claims 1-3, wherein said mancozeb slurry is obtained by a first drying step which comprises either spray drying an initial slurry or drying the initial slurry in a rotary vacuum dryer.
5. The process as claimed in claim 4, wherein said initial slurry has a moisture content of from about 10% to about 55% by weight.
6. The process as claimed in any preceding claim, wherein said process step of continuously drying the mancozeb slurry is carried out in a provided paddle dryer, said provided paddle dryer comprising a jacket which has temperature maintained from about 80°C to about 120°C using pressurized steam at a pressure of from about 0.8 kg/cm2 to about 1.5 kg/cm2.
7. The process as claimed in any preceding claim, wherein said process step of continuously drying the mancozeb slurry is carried out in a provided paddle dryer by conductive heating.

8. The process as claimed in any preceding claim, wherein said controlled vacuum comprises a low pressure atmosphere of nitrogen gas maintained throughout the paddle dryer and paddle cooler.
9. The process as claimed in claim 8, wherein said low pressure of nitrogen comprises nitrogen gas at a pressure of about 500 mm to about 700 mm of Hg column.
10. The process as claimed in any preceding claim additionally comprising feeding hot mancozeb slurry under said controlled vacuum in the paddle dryer; allowing the fed mancozeb slurry to churn and move inside said paddle dryer; and allowing the hot dried mancozeb powder to continuously move out of said paddle dryer into a provided paddle cooler.
11. A process for drying a wet mass of mancozeb slurry to mancozeb powder having moisture content less than 1% by weight, said process comprising:

(a) feeding a provided wet mass of mancozeb slurry having predetermined moisture content to a provided continuous paddle dryer within a provided drying system;
(b) drying said fed mancozeb slurry in said provided continuous paddle dryer at a temperature of from about 80°C to about 120°C;
(c) conveying hot dried mancozeb powder from said continuous paddle dryer and feeding said hot dried mancozeb powder to a provided paddle cooler;
(d) circulating a coolant fluid within said paddle cooler thereby cooling said fed hot dried mancozeb powder within the paddle cooler at a controlled vacuum of from about 500 mm Hg to about 700 mm Hg;
(e) separating and collecting fine particles of dried mancozeb in a provided fines separator and conveying the collected particles to a provided fluid scrubber;
(f) contacting said collected fine particles of mancozeb particles to a cooling fluid within said fluid scrubber;

(g) optionally recycling said cooled fine mancozeb powder particles into a
provided drying system; and (h) conveying the remaining dried and cooled mancozeb powder out of said
drying system to a plurality of external packaging locations.
12. A system for drying a wet mass of mancozeb slurry to obtain dried mancozeb
having moisture content less than about 1%, said system comprising:
(a) an inlet capable of feeding a provided wet mass of mancozeb slurry having predetermined moisture content to a provided continuous paddle dryer;
(b) a continuous paddle dryer comprising a jacket which has temperature maintained from about 80°C to about 120°C using pressurized steam at a pressure of from about 0.8 kg/cm2 to about 1.5 kg/cm2, said continuous paddle" dryer additionally comprising a plurality of substantially hollow paddles mounted onto a motor driven central shaft and adapted to rotate at a controlled speed of rotation; and
(c) a paddle cooler comprising a cooling jacket and a plurality of hollow paddles mounted on a motor driven central shaft, said paddle cooler comprising an inlet means connected to the paddle dryer outlet and capable of receiving the hot dried mancozeb powder and carrying the received hot dried mancozeb powder within the paddle cooler, said paddle cooler further comprising a coolant circulation means comprised within said paddle cooler which is capable of circulating a chilled fluid throughout the paddle cooler; and
wherein said paddle dryer is maintained at a controlled vacuum of from about 500 mm Hg to about 700 mm Hg.
13. The system as claimed in claim 12, wherein said paddle dryer additionally
comprises a paddle dryer outlet which receives the hot dried mancozeb powder

from the paddle dryer and feeds the received hot and dried mancozeb powder to a provided paddle cooler.
14. The system as claimed in claim 12 or claim 13, wherein said paddle cooler additionally comprises at least one paddle cooler outlet which conveys the dried and cooled mancozeb powder out of the drying system to a plurality of external packaging locations.
15. The system as claimed in claims 12-14 additionally comprises a fines separator comprising a cyclone and a bag filter having sufficiently high surface area capable of collecting fine particles of mancozeb and conveying the collected fine particles to a chilled fluid scrubber.
16. The system as claimed in claim 15, wherein said chilled 0uid scrubber is a chilled water scrubber.
17. The system as claimed in claim 15 or claim 16, wherein said chilled water scrubber collects fine particles of mancozeb; contacts the collected particles to the chilled fluid being circulated through the paddle cooler; and conveys the collected fine cooled mancozeb particles to the recycling means which recycles the fine particles into a provided drying system.
18. A system for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1%, said system comprising:

(a) an inlet capable of feeding a provided wet mass of mancozeb slurry having predetermined moisture content to a provided continuous paddle dryer;
(b) a continuous paddle dryer comprising a jacket which has temperature maintained from about 80°C to about 120°C using pressurized steam at a pressure of from about 0.8 kg/cm2 to about 1.5 kg/cm2, said continuous paddle dryer additionally comprising a plurality of substantially hollow

paddles mounted onto a motor driven central shaft and adapted to rotate at a controlled speed of rotation;
(c) a paddle dryer outlet capable of receiving the hot dried mancozeb powder from the paddle dryer and feeding said hot dried mancozeb powder to a provided paddle cooler;
(d) a paddle cooler comprising a cooling jacket and a plurality of hollow paddles mounted on a motor driven central shaft, said paddle cooler comprising an inlet means connected to the paddle dryer outlet and capable of receiving the hot dried mancozeb powder and carrying the received hot dried mancozeb powder within the paddle cooler, said paddle cooler further comprising a coolant circulation means comprised within said paddle cooler which is capable of circulating a chilled fluid throughout the paddle cooler, said paddle dryer being maintained at a controlled vacuum of from about 500 mm Hg to about 700 mm Hg;
(e) a fines separator comprising a cyclone and a bag filter having sufficiently high surface area capable of collecting fine particles of mancozeb and conveying said collected fine particles to a chilled water scrubber;
(f) a chilled water scrubber for collecting fine particles of mancozeb and contacting said collected particles to the chilled fluid being circulated through the paddle cooler and thereafter conveying the collected fine cooled mancozeb particles to be recycled into the drying system; and
(g) a paddle cooler outlet capable of conveying the remaining dried and cooled mancozeb powder out of said drying system to a plurality of external packaging locations.
19. The system as claimed in claims 12-18, wherein said paddle dryer additionally comprises at least a product filer, a condenser, a receiver and at least one vacuum pump which is capable of maintaining a controlled vacuum of from about 500 mm Hg to about 700 mm Hg.

20. The system as claimed in claims 12-19, wherein said paddle dryer additional comprises an outlet means for carrying the moisture generated during drying of said moist mancozeb powder and releasing the moisture generated thereby to the external environment.
21. The system as claimed in claim 12-22, wherein said paddle dryer is fabricated from stainless steel.
22. A continuous process for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1% substantially as described herein.
23. A system for drying a wet mass of mancozeb slurry to obtain dried mancozeb having moisture content less than about 1% substantially as described herein.