Claims:1. A continuous drying process for producing a lump free dry powder of metformin or acetaminophen or their granulate composition by spin flash drying process comprising the steps of:
a) feeding the wet cake of metformin or acetaminophen or their granulate composition having moisture content between 5-15% w/w through screw feeding unit rotating at a speed ranging between 500-1500rpm
b) contacting said material with a clean hot air stream of temperature ranging between 70ºC and 130ºC
c) adjusting the continuous feed material and drying capacity of introduced hot air by controlling the drying of the powder to desired moisture content of less than 0.5% w/w.
2. The process according to claim 1 where in the wet cake of metformin or acetaminophen or their granulate has a moisture content of 5-10%w/w
3. The process according to claim 1, involving a process of hot air lifting the wet cake fed in to a Spin Flash Dryer by the drying hot air flow against the gravitational force.
4. The dry powder of metformin or acetaminophen or their granulate obtained by Spin Flash Dryer according to claim 1 has a moisture content ranging between 0.1 to 0.5% w/w
5. The Spin Flash Dryer equipment (Fig.1) used for continuous drying process for metformin or acetaminophen or their granulate composition according to claim 1 comprising:
1. feeder for wet cake with variable speed drive screw conveyer
2. aperture for supply of clean hot air
3. vertical, cylindrical dryer chamber with bottom (3a), middle (3b) and top(3c) sections
4. air powder separator for separating the particles from drying gas
5. rotary air lock valve (RAV) for unloading the dried material
6. aperture for removal of the dried material.
7. aperture for the removal of the spent drying air
8. suction fan for removal of gases

6. The process for producing dry powder of metformin or acetaminophen or their granulate compositions by spin flash drying process according to claim 1, where in the clean hot air stream used in step (b) is generated through the steam radiator which is affixed with HEPA filters.
7. The HEPA filter used in spin flash drying process according to claim 6 are with 2-10 microns filters.
, Description:FIELD OF THE INVENTION
The present invention relates to continuous drying process for metformin, acetaminophen or their granulate composition materials.

BACKGROUND OF THE INVENTION
Drying process for active pharmaceutical ingredients and their granulate composition on the commercial scale gained significant values owing to concerns like handling of dry powder compliance to regulatory requirement, contamination concerns owing to air quality and time required for commercial drying process etc.
Continuous drying process for the active ingredients has been reported by various means and type of equipment, however, particular suitability for various drying materials like pastes, filter cakes and semi dried material remained still matter of larger concern, since suitability of the material with respect to drying process depends on various physical and chemical properties of the active materials kept under drying.
Metformin (has melting point of exceeding 200ºC) is a well-known commercial biguanide class of oral anti hyperglycemic medication used as the first-line medication for the treatment of type 2 diabetes, particularly in people who are overweight. It is chemically termed as N,N-Dimethylimidodicarbonimidic diamide and structurally represented by the following structure:

Similarly, another large volume active pharmaceutical -Acetaminophen also known as Paracetamol or APAP (melting point of exceeding 170ºC) is a non-salicylate antipyretic and non-opioid analgesic agent used to treat pain and fever. It is chemically termed as N-acetyl-p-aminophenol and structurally represented by the following structure:

Both these products appear to be suitably dried at higher temperatures to get a commercially available dried material by continuous drying process, however, type of equipment and drying conditions desired for making a commercially viable continuous process are not reported so far specifically for these APIs.
Conventional drying process is a mass transfer process consisting of the removal of water or solvent by evaporation from a solid, semi-solid or liquid. The process is used as a final production step before selling or packaging products. Various drying process and apparatus have been used in the past for the drying of different materials.
Risenby, et al in U.S. Patent No. 4,581,830 describes an apparatus for fluid-bed drying, particularly for simultaneous drying and disintegration of a material in the form of a paste.
However due to fluidized state, the particles are subjected to a turbulent state and there is a high possibility of product loss. There are observed more tendencies of sticking of the particles to the bed creating lumps in the dried product, hence, render process unsuitable for commercial drying.
Getler, et al in U.S. Patent No. 6,085,440 describes a process for drying of pastes and filter cakes into a powder with a desired mean particle size using Spin Flash Dryer. Two classifiers are arranged in the apparatus to obtain desired mean particle. The particles remain in the drying zone until they obtain the desired particle size. The disclosure in this patent specifically relates to products preferably dried according to this invention are fruit and beet pulps, distillers residues, pesticides, pigments, dyes, ceramics, active coal, sludge and zeolites.
Christensen, et al in U.S. Patent No. 9,851,147 describes a typical Spin Flash Dryer for use in the field of food waste disposal comprising a waste outlet arranged in a chamber bottom of the Spin Flash Dryer for removal of a residual organic waste material.
Hence, conventional Spin Flash Drying is generally in line with upright fluidized bed structure. A drying agitator works as rotor for the breaking lumps and hot air goes into reasonably elevated velocities for providing dynamic actions for disintegrating and drying the products. Fresh air can be sucked through hot air producers which can be direct and indirect in the nature. The admission for drying the chambers is peripheral for providing whirling air suctions across the dryer.
A general screw conveyer forces material towards the drying chambers, that has the rotor provided from bottom, which is a specially made scrapper disintegrators and blades to break lumpy mass for smaller fragments.
The lumps which are broken using rotor start drying and also simultaneously disintegrate with the stream of hot air.
The airborne powder particles get persisted on top of the drying chambers that pass through the classifier that classifies it into desired sizes. The particles with bigger diameters return to chambers, while fine travels with the air for final collection through retract pulse filters through which maximum of powder recovery can be accomplished.
Despite various disclosures related to drying of the various powders and products, the design of the dryer besides suitability of the product may leads to various hurdles to achieve a continuous drying process for the pharma actives and products.
Also, conventional Spin Flash Dryer also have concerns of use of quality of hot air from suction, the optimum parameters desirable for continuous drying and avoiding any lump formation or agglomeration of the powder material etc.
Still there remains a need to develop a simple, continuous drying process which is commercially viable and amenable to scale up for drying of products like metformin or acetaminophen or similar higher melting active pharmaceutical ingredients or their granulate compositions with desirable moisture content and devoid of lumps, or related concerns.
Accordingly, the present inventor have surprisingly found that modified spin flash drying equipment and process with a provision of clean hot air stream of temperature ranging between 70ºC and 130ºC suitably produces lump free dry powder of high melting actives (>150ºC) viz, metformin or acetaminophen or their granulate compositions with desirable moisture content.

SUMMARY OF INVENTION
In one aspect according to the present invention, it relates to continuous drying process for producing a lump free dry powder of metformin or acetaminophen or their granulate composition by spin flash drying process comprising the steps of:
a) feeding the wet cake of metformin or acetaminophen or their granulate composition having moisture content between 5-15% w/w through screw feeding unit rotating at a speed ranging between 500-1500rpm
b) contacting said material with a clean hot air stream of temperature ranging between 70ºC and 130 ºC.
c) adjusting the continuous feed material and drying capacity of introduced hot air by controlling the drying of the powder to desired moisture content of less than 0.5% w/w.
In a particular aspect, according to the present invention, it relates to Spin Flash Dryer (hereinafter referred as SFD) equipment (Fig.1) for continuous drying process for pharmaceutical active ingredients viz, metformin or acetaminophen or their granulate composition comprising:
1. feeder for wet cake with variable speed drive screw conveyer
2. aperture for supply of clean hot air
3. vertical, cylindrical dryer chamber with bottom (3a), middle (3b) and top(3c) sections
4. air powder separator for separating the particles from drying gas
5. rotary air lock valve (RAV) for unloading the dried material
6. aperture for removal of the dried material.
7. aperture for the removal of the spent drying air
8. suction fan for removal of gases
BRIEF DESCRIPTION OF THE DRAWINGS
Fig.1: Exemplary Spin Flash Dryer (SFD) equipment for commercial continuous drying process of solid materials (>150 ºC) to collect dry powders continuously.
DETAILED DESCRIPTION
As set forth herein, embodiment provides continuous drying process of high melting actives (>150ºC) viz, metformin or acetaminophen or their granulate composition materials.
In one embodiment the present invention provides a continuous drying process of Metformin or acetaminophen or their granulate composition materials with Spin Flash Dryer.
The Spin Flash Dryer (SPD) is a continuous bulk drying system which helps in energy savings, low labour deployment, uniform quality products, low space requirement and minimal dusting due to negative pressures in the system during drying.
In another embodiment according to present invention it provides a continuous drying process for producing a lump free dry powder of metformin or acetaminophen or their granulate composition materials.
In a particular embodiment according to present invention Spin Flash Drying process comprising the steps of:
a) feeding the wet cake of metformin or acetaminophen or their granulate composition having moisture content between 5-15% w/w through screw feeding unit rotating at a speed ranging between 500-1500rpm
b) contacting said material with a clean hot air stream of temperature ranging between 70ºC and 130 ºC
c) adjusting the continuous feed material and drying capacity of introduced hot air by controlling the drying of the powder to desired moisture content of less than 0.5% w/w.
In one embodiment the wet cake of metformin or acetaminophen or their granulate composition used for spin flash drying has a moisture content of 5-10%w/w
In another embodiment the Spin Flash Dryer process involves clean hot air for lifting the wet cake fed in to a Spin Flash Dryer by the drying hot air flow against the gravitational force.
In a preferred embodiment the dry powder of metformin or acetaminophen or their granulate compositions obtained by Spin Flash Dryer has a moisture content ranging between 0.1 to 0.5% w/w.
The term granulate composition used in the specification relates to pharmaceutical compositions derived using pharmaceutical acceptable carrier/excipients.
In a particular embodiment, according to the present invention, it relates to Spin Flash Dryer (SFD) (Fig.1) for continuous drying process for metformin or acetaminophen or similar or their granulate composition containing:
1. feeder for wet cake with variable speed drive screw conveyer
2. aperture for supply of clean hot air
3. vertical, cylindrical dryer chamber with bottom (3a), middle (3b) and top(3c) sections
4. air powder separator for separating the particles from drying gas
5. rotary air lock valve (RAV) for unloading the dried material
6. aperture for removal of the dried material.
7. aperture for the removal of the spent drying air
8. suction fan for removal of gases
Further the clean hot air generator is a steam radiator, which is affixed with HEPA filters of 2-10 microns in order to ensure microbial free clean air.
EXAMPLES:
The following examples further describe and demonstrate particular embodiments within the scope of the present invention. It will be apparent to those skilled in the art that many modifications, both to materials and methods, may be practiced without departing from the scope of the invention.

Example 1: Continuous drying process of Metformin:
The wet reaction mass was received from crystallization reactor into agitated Nutsche Filter and drier in which mother liquor was simultaneously drained by gravity. To this less than 600 mmHg (600-0 mmHg) vaccum was applied for 20-50 minutes to suck the additional mother liquor. Nitrogen pressure of not more than ~2000 mmHg was also applied for about 30-60 minutes to drain the Mother liquor.
The cake obtained was washed with 1500±200lit aq. methanol solution from crystallizer reactor and agitated for 10-15 minutes to make slurry. Mother Liquor was drained by gravity followed by vaccum of less than 600 mmHg (600-0 mmHg) for 30-60 minutes and later on nitrogen pressure of not more than ~2000 mmHg was applied for 20-50 minutes to drain the mother liquor.
The obtained cake was again subjected to wash with 1500±200lit aq. methanol solution and was agitated for 10-15 minutes to make slurry. Mother liquor was drained by gravity followed by vacuum of less than 600 mmHg (600-0 mmHg) for 30-60 minutes and later on nitrogen pressure of not more than ~2000 mmHg was applied for 20-50 minutes to drain the mother liquor.
Lateron , in Nutsche Filter, hot water circulation was applied to semidry the material until hot water outlet temperature is 75-98 °C. This temperature was maintained for 1hr 30 minutes ± 30 minutes under vaccum for less than 600 mmHg (600-0 mmHg). The obtained cake had a moisture content of 5-10%w/w
Now, the drying process is carried out in specific designed Spin Flash Dryer (SPD) according to the present invention for producing a dry powder.
Accordingly, firstly the empty run of Spin Flash Dryer(SFD) was performed causing raise in the temperature of about 130ºC , followed by the material unloading from agitated Nutsche Filter and loaded continuously to Spin Flash Dryer through controlled screw feeding unit rotating at a speed ranging between 500-1500rpm.
The inlet air temperature was adjusted at 70-120°C and the continuous drying process of the cake was performed to obtain a dried powder of metformin continuously with a moisture content ranging between 0.1 to 0.5% w/w.
In one of the commercial drying process run according to the present invention, the said desired Spin Flash Dryer performed 5 hours of continuous running drying process to provide about 5000kgs of dried metformin (having moisture content <0.5%w/w).

Example 2: Drying process of Acetaminophen:
The drying process for Acetaminophen is carried out in Spin Flash Dryer according to the present invention for producing a pharmaceutic grade dry powder.
Firstly, the empty run of Spin Flash Dryer was performed causing raise in the temperature of about 130ºC with hot air, followed by semi-dried acetaminophen material (moisture content ranging 2-10%w/w) was loaded continuously to Spin Flash Dryer through controlled screw feeding unit rotating at a speed ranging between 500-1500rpm.
The HEPA clean inlet air temperature was adjusted at 80°-130°C and the continuous drying process of the cake was performed to obtain a dried powder of acetaminophen continuously with an achieving moisture content ranging between 0.1 to 0.4% w/w.
In one of the commercial run, the said desired Spin Flash Dryer performed 4 hours of continuous running drying process to provide 3000kgs of dried Acetaminophen.

While the foregoing pages provide a detailed description of the preferred embodiments of the invention, it is to be understood that the summary, description and examples are illustrative only of the core of the invention and non-limiting. Furthermore, as many changes can be made to the invention without departing from the scope of the invention, it is intended that all material contained herein be interpreted as illustrative of the invention and not in a limiting sense.