Title of Invention

"A PROCESS FOR PREPARATION OF SPHERICAL NITROCELLULOSE GRANULES"

Abstract

This invention relates to a process for preparation of spherical nitrocellulose granules comprising of gelling 50g wet fibrous nitrocellulose, characterised by adding 5.5g nitroglycerine desensitized with 210ml ethyl acetate, adding 1.5g stabilizer as herein described emulsifying the gel in water, coating the nitrocellulose globules with animal glue such as herein described removing the solvent by distillation at 45°C, dehydrating using sodium sulphate by osmosis, heating to remove traces of solvent, separating wet spheres by sieving and finally drying in steam heated oven wherein said fibrous Nitrocellulose (NC) taken has preferably nitrogen content around 12.2% and moisture content around 30%, the viscosity of gel obtained by said gelling of fibrous nitrocellulose with ethyl acetate, is kept preferably at 30,000+3000 cp at 25°C.

Full Text

FIELD OF INVENTION This invention relates to an improved process for preparation of spherical nitrocellulose granules for propellants, particularly for composite modified double based propellants. PRIOR ART The composite modified double based (CMDB) propellant contains substantial amount of nitrocellulose and is made by casting a dough of Nitrocellulose, Ammonium Perchlorate, Aluminium powder, Nitroglycerine and other plasticisers. The fibrous nitrocellulose used in preparation of the propellant has certain disadvantage. Firstly the loadabiliry of solids in casting liquid is reduced considerably. Another disadvantage of using fibrous nitrocellulose is that the pot life of the dough becomes very short due to instant absorption of nitroglycerine in nitrocellulose thereby creating problems of processing. According to a process known in the art (US Patent 2,027,114), and subsequently U.S. Patents Nos. 2,111,075, 2,175,212 and 2,206,916, globular smokeless powder is prepared by a process comprising, dissolving a smokeless powder base as nitrocellulose having nitrogen content of 12.4 to 13.4 in a volatile solvent such as ethyl acetate, agitating the solution with an excess of a non-solvent vehicle in the presence of a protective colloid and heating the vehicle to the vapourising point of the solvent during agitation. The disadvantage of this process is that the particle size obtained of nitrocellulose is between 400-750 µ, . Another disadvantage of the above process is that the powder is not kept spherical but flattened to a constant thickness of about 0.03- inch Yet another disadvantage is that the powder requires to be further, treated with nitroglycerine and other plasticiser for surface perretrafrorr. According to another process spherical nitrocellulose is prepared by fluid ball casting powder method. The process begins with the preparation of nitrocellulose lacquer which contains all of the constituents (stabiliser, plasticiser, incorporants etc.) of the final product. When a lacquer of a desired composition and consistency has been prepared, the next step is to reduce' this to a fine state of division as discreet lacquer particles suspended with a carrier liquid. This is accomplished into a graining chamber, where particle size and distribution is controlled. In passing from the graining chamber to the solvent removal operation, any water entrapped in the lacquer particles is removed. As the solvent is distilled from the lacquer particles, the product remaining, consists of dense, fully colloid spheres of nitrocellulose. The disadvantage of this method is that the particle size varies between 10 to 150 µm, which is a very wide range. Another disadvantage of this method is the use of diaphenylamine as a stabiliser in a double base composition of nitrocellulose and nitroglycerine which is not very effective for the stability of the fluid ballcasting powder. OBJECTS OF PARESENT INVENTION > \ * The primary object of the present invention is to propose a process for the preparation of compact, transparent and spherical nitrocellulose granules particularly for composite modified double based propellants. Another object of the present invention is to propose a process which provides nitrocellulose granules having high' packing density of 0.94 g/ml. Still another object of the 'present invention is to propose a process which provides nitrocellulose granules having high loadability in the CMDB class of propellants. Further object of the present invention is to propose a process which provides nitrocellulose granules, the use of which can adjust the pot life of the CMDB propellant casting. Still further object of the present invention is to propose a process which has no fire hazard as it is carried out in water wet conditions. Further object of the present invention is to propose a'process which provides'higher yield of nitrocellulose of the order of 90-95%. Still further object of the present invention is to propose a process which provides nitrocellulose granules having higher energy because of incorporation of nitroglycerine. Yet further object of the present invention is to propose a process which provides nitrocellulose granules, which facilitate further absorption of nitroglycerine while casting a CMDB propellent. STATEMENT OF INVENTION According to this invention there is provided a process for preparation of spherical nitrocellulose granules comprising of gelling wet fibrous nitrocellulose with ethyl acetate, adding nitroglycerine desensitised with ethyl acetate addition of a stabiliser, emulsifying the gel in water, coating the nitrocellulose globules with animal glue, removing the solvent by distillation, dehydrating using sodium sulphate by osmosis, heating to remove traces of solvent, separating wet spheres by sieving and finally drying in steam heated oven. STATEMENT OF INVENTION The present invention relates to an improved process for preparation of compact, transparent and spherical nitrocellulose granules having high packing density, high energy higher loadability and increased pot life. This process consists of gelling wet fibrous nitrocellulose having nitrogen around 12% with ethyl acetate. Nitroglycerine desensitised with ethyl acetate and carbamite as stabiliser are added to the gel The gel is emulsified in water using a dispensor which cuts the gel into globular form. The mix is passed 7-10 times through dispensor to get the desired size of globules. The solvent from the emulsion is removed by distillation at around 45°C, then around 68°C and finally to around 77°C to remove even the traces of solvent. The size of NC granules ranges from 10 µ to 90 µ with maximum yield being between 3()-40 µ. The yield achieved is 90-95%. In the present process, gel preparation and emulsion making is carried out in one vessel only. Also the solvent removal is carried out by equilibrium distillation keeping the liquid and vapour in equilibrium. The distillation is carried out using internal condensing system by disturbing the equilibrium very slightly between the liquid and vapour. The energy content of spherical nitrocellulose alone with 2.5% of carbamite as stabilizer is about 790 cal/gm, but when incorporated with 7.5% of nitroglycerine, it enhances by about 60 cal/gm. According to present invention spherical nitrocellulose granules are prepared by a process comprising of gelling wet fibrous nitrocellulose (moisture content 30%) preferably having around 12.2% nitrogen content with ethyl acetate. The viscosity of this gel is kept at 30,000 ±3000 cp at around 25°C. Requisite amount of nitroglycerine desensitised with ethyl acetate and carbamite as stabiliser are added to the gel. The gel is then emulsified in water using a disperser in-line, which cuts the gel in very fine globular form The size of these globules is entirely the function of viscosity of the gel, amount of dispersing medium and the type of disperser. The type and speed of the disperser also play a vital role in the uniformity and the size of the globules. In the present process, the gel and the emulsifying medium (water) are passed through the disperser having an emulsor screen as a stator. The mix is passed through the disperser for 7 to 10 times to ensure proper emulsion with desired size of the globules. The globules of nitrocellulose are coated with animal glue to prevent them from joining. The solvent from the emulsion is slowly removed by distillation at around 45°C initially to keep the globular shape intact. After about 40% removal of solvent, the globules are dehydrated from their core .using sodium sulphate solution by osmosis. Later, the temperature of the contents is slowly raised to around 68°C to remove most of the solvent from the globules. The hard spheres are then subjected to further heating around 77°C for the removal of traces of solvent and then separated by wet sievng through a 90 µ (170 BSS) sieve to obtain average particle size of 35±10 µ. The particles range between lO µ/and 90 µ with maximum yield of particles between 30 µ and 40 µ. These spheres are then separated from water and dried in steam heated oven at around 55°C to 3-5% moisture content. The yield achieved is 90-95%. WORKING EXAMPLE The process of the present invention will now be illustrated with a working example which is intended to be a typical example to illustrate the working of the invention and is not intended to be taken restricitvely to imply any limitation on the scope of the invention. For the preparation of spherical nitrocellulose 50 g of fibrous nitrocellulose was used . « Raw Materials used: 1. Fibrous nitrocellulose (wet) 50 g (dry weight) Type A; N content 12.2% (moisture content 30%) 2. Nitroglycerine 5.5 g 3. Diethyldiphenyl urea (carbamite) 1.5 g (stabiliser) 4. Ethyl acetate 210 ml (solvent) 5. Gelatine (food grade) 15 g (protective coating agent) 6. Sodium sulphate 40 g (dehydrating agent) 7. Dioctyl Sodium Sulphosuccinate (DOT) 0.2 g (surface active agent) 8. Katrang S.D. 1 ml (antifoaming agent, if required) 9. Process water 1540ml (dispersing medium) The spherical nitrocellulose was prepared as follows: Step I 1.5 gm of diethyl phehyl urea (carbamite) as stabiliser was dissolved in 130 ml of ethyl acetate (solvent) by stirring. About 25 gm (dry basis) of wet fibrous nitrocellulose (Type A; N content 12.2%) was added to the above solution to form a soft bed, 5.5 gm of nitroglycerine was then dissolved in 40 ml of ethyl acetate and was added to the soft bed. The remaining 25 gm (dry basis) of wet fibrous nitrocellulose was added to this bed and stirred. The viscosity of this gel at 25°C was about 30,000 ± 3,000 cp. Step II Gelatine (protective coating agent) solution was prepared by dissolving 15 gm of gelatine (food grade) in 170 ml of water at 35°C. Step III Dioctyl sodium sulphosuccinate (DOT) (surface active agent) solution was prepared by dissolving 0.2 g DOT into 40 ml of water. Step IV The nitrocellulose gel solution prepared in Step I was stirred continuously at 33°C and the DOT solution prepared in Step III was added to it. The surface tension of the gel immediately reduces and the viscosity of the gel tails below 100 cp. While the nitrocellulose gel was kept stirred at 33°C, gelatine solution prepared in Step II was added and then 170 ml of water was added to it. StepV The whole mass of nitrocellulose gel was then passed through a dispersor and a fine emulsion of nitrocellulose globules dispersed in water was obtained. Step VI The emulsion of nitrocellulose globules obtained in Step V was then transferred to a distillation unit having 1200 ml of water saturated with 45 ml of ethyl acetate, kept stirred at 35°C. Step VII A solution of sodium, sulphate (dehydrating agent) of specific gravity 1.18 at 25°C, was prepared by dissolving 40 gm of sodium sulphate in 200 ml of water. Step VIII Distillation of Step VI, initially was carried out slowly to distill off ethyl acetate. When about 40% of the solvent, ethyl acetate was recovered, sodium sulphate solution, prepared in Step VII was added slowly to the distillation vessel. This removes the water entrapped in the semi hardened globules of nitrocellulose by osmosis. Then raised the temperature slowly to reach to 68°C and about 90% of ethyl acetate was recovered. Step IX The contents were discharged in about 400 ml of cold water and the mass was allowed to settle. Supernatent liquid was decanted and the mass was heated to. about 77°G with 300 ml of fresh water, to remove the traces of solvent, gelatine, sodium sulphate and DOT. StepX The mass was sieved through a 170 BS sieve. The material passing through the sieve was then filtered and dried in a steam heated oven at 55°C to a moisture content of 3-5%. The specification of spherical nitrocellulose prepared by the process of present invention were as follows:- (Table Removed) This process of making spherical nitrocellulose is very economical on commercial scale as the solvent is reused. The globules of nitrocellulose prepared are spherical, homogene.ous, compact and transparent white in colour, having average particle size of 35 ± 10 µ. The product has a high bulk density of 0.94 gm/cm3 and gives a calorimetric value of 850 ± 20 cal/gm. The yield is more than 90%. It is to be understood that the.inhibition formulation and process for preparation thereof as described in the present invention is susceptible to changes, adaptations, modifications by those skilled in the art. Such modifications,'changes, adaptations are intended to be within the scope of the present invention which is further set forth under the following claims: WE CLAIM: 1. A process for preparation of spherical nitrocellulose granules comprising of gelling 50g wet fibrous nitrocellulose, characterised by adding 5.5g nitroglycerine desensitized with 210ml ethyl acetate, adding 1.5g stabilizer as herein described emulsifying the gel in water, coating the nitrocellulose globules with animal glue such as herein described removing the solvent by distillation at 45°C,.dehydrating using sodium sulphate by osmosis, heating to remove traces of solvent, separating wet spheres by sieving and finally drying in steam heated oven wherein said fibrous Nitrocellulose (NC) taken has preferably nitrogen content around 12.2% and moisture content around 30%, the viscosity of gel obtained by said gelling of fibrous nitrocellulose with ethyl acetate, is kept preferably at 30,000+3000 cp at 25°C. 2. The process as claimed in claim 1, wherein said stabilizer is carbamite. 3. The process as claimed in claim 1, wherein said heating after dehydration by osmosis, is carried out firstly at round 68°C followed by heating around 77°C. 4. The process as claimed in claim 1, wherein said final drying in steam heated oven is preferably at around 55°C till moisture content is reduced to 3 to 5%. 5. The compact, transparent spherical nitrocellulose granules with high pack density, high energy and with average particle size between 30 to 40 microns as prepared by the process substantially described and illustrated herein. 6. The process for the preparation of spherical nitrocellulose granules substantially as herein described.

Documents:

1178-del-2000-abstract.pdf

1178-del-2000-claims.pdf

1178-del-2000-correspondence-others.pdf

1178-del-2000-correspondence-po.pdf

1178-DEL-2000-Description (Complete).pdf

1178-del-2000-form-1.pdf

1178-del-2000-form-19.pdf

1178-del-2000-form-2.pdf

1178-del-2000-form-26.pdf

1178-del-2000-form-4.pdf