FORM 2
THE PATENTS ACT, 1970
(Act 39 of 1970)
COMPLETE SPECIFICATION
(See Section 10)
Title: "An improved process for manufacturing cold water soluble Methyl Cellulose"
Name: M/s. Gujarat Alkalies and Chemicals Limited.
Address: P.O. Petrochemicals - 391 346,
Dist: Vadodara, Gujarat - India.
Nationality: Indian
The following specification particularly describes the invention and the manner in which it is to be performed.

Title of the Present Invention
An improved process for manufacturing cold water soluble Methyl Cellulose
Field of the Present Invention
This invention relates to an improved & economical industrial process for manufacturing low viscosity cold water soluble Methyl Cellulose suitable for pharmaceutical application.
Background of the Present Invention
Methyl Cellulose is a valuable product and is used variedly in Pharmaceutical industry, Food Industry and many more. IN 189589 has disclosed the preparation of the low viscosity cold water soluble Methyl Cellulose conforming to all laid down pharmacopoeia specifications and suitable for tablet coating purpose
The preparation of alkali cellulose is very important to the overall process and the quality of the final product. Known methods of preparing Alkali Cellulose are, US 1,999,043 reported that the cellulose sheets are steeped in alkali liquor followed by pressing of the same to expel the excess liquid. US 2,145,862 has disclosed the preparation of Alkali Cellulose at 55 - 144°C using 60 - 80% Caustic solution.
Flaws with such method is that the use of large quantity of caustic lye during alkali cellulose formation may result in to the partial hydrolysis of Methyl Chloride leading to slow rate of reaction and formation of more side products during etherification. The uniformity in the alkalization is one of the controlling factors for achieving uniformly substituted water soluble Methyl Cellulose. The presence of excess alkali with alkali cellulose mass give rise to the undesirable side products during the etherification eventually affecting the rate of etherification.
The process of manufacturing Methyl Cellulose in accordance with the present invention discloses a method of preparing the alkali cellulose that is simple, easy to operate at industrial scale and the alkali cellulose thereof prepared is suitable for etherification. The process does not use caustic bath, any solvents, catalyst and the reaction is performed at very mild temperature conditions.
There are several problems associated with the reaction conditions and reactant ratios reported in the literature. In the absence of proper reactant ratio and reaction temperature both vapor and liquid phase methylation, gives non uniformly substituted product not meeting the pharmacopoeia specifications with respect to 2% solution clarity.
Further, Dimethyl Ether is formed as a by- product but in prior art processes no attention as such has been given on this aspect.

Summary of the Present Invention
The present invention relates to an improved process for manufacturing cold water soluble Methyl Cellulose comprising of the step of Alkali Cellulose formation by reacting Cellulose powder with Caustic Lye under inert atmosphere and efficient stirring; the step of charging liquid Methyl Chloride in a pre-eooled reactor; the step of reacting the Alkali Cellulose mass with the charged liquid Methyl Chloride, the step of recovering excess liquid Methyl Chloride for recycling the same in the process, the step of slurring the crude product in hot water having minimum 90 °C temperature; the step of centrifuging the slurry with simultaneous washings with hot water having minimum 90 °C temperature; and finally the steps of drying, pulverizing and sieving the final product.
Various parameters like the reactant ratios, temperature, pressure and down stream processing have been modified / improved in a such way that the process is very easy to operate at the semi - commercial / commercial scale with the desired specifications of the final product obtained in > 90% of the theoretical value.
The process of manufacturing Methyl Cellulose in accordance with the present invention neither requires large quantity of caustic lye nor any solvent during the methylation and reactions are performed at very low temperature to give high yield with minimum formation of undesirable side products. The final product, Methyl Cellulose, so obtained has been found to be suitable for tablet coating purpose.
The methylation carried out in the gas phase normally produces non-uniformly substituted product, not meeting the pharmacopoeia specifications with respect to 2% Solution clarity. The process of manufacturing Methyl Cellulose in accordance with the present invention, methylation has been designed in the liquid phase. The quantity of liquid Methyl Chloride taken also plays a very important role in the reaction & the quality of final product.
The process of manufacturing Methyl Cellulose in accordance with the present invention exclusively utilizes Methyl chloride both as reaction media & reactant, restricts the formation of Dimethyl ether - a by product to < 3% per cycle of Methyl Chloride used in the methylation and effectively utilizes the recovered Methyl chloride in the process. The process does not use any solvent in the reaction. The recovered methyl chloride may be used as such or as a blend with fresh / pure methyl chloride. Furthermore, there is no prior art suggested for such recycling of Methyl chloride.
The process of manufacturing Methyl Cellulose in accordance with the present invention discloses the processing of the crude material in the final stages with hot water, that has been standardized in such a way that the final product does not contain more than 0.5 % Chloride content, which is the requirement of the pharmaceutical grade product.
Over & above, the present invention provides an easy process to operate at this scale since most of the process steps are carried out in the same reactor system.

Detailed Description of the Present Invention
The process of manufacturing Methyl Cellulose in accordance with the present invention has successfully modified / improved the earlier reported process at small scale and has provided an economical industrial process for preparing low viscosity, cold water soluble Methyl Cellulose conforming to all the laid down pharmacopoeia specifications and can be used for tablet coating.
The process of manufacturing Methyl Cellulose in accordance with the present invention consists of several controlling factors whose proper matching is required at the higher scale of operation in order to minimize the process related obstacles/problems so as to make the process more economical.
The complexity in the alkali cellulose formation, partial hydrolysis of methyl chloride primarily responsible for the formation of side products & formation of non - uniform product are more pronounced at the higher scale of operation. Hence, proper care should be taken while carrying out each step.
The process of manufacturing Methyl Cellulose in accordance with the present invention has the following steps.
Stepl:
In the first stage the alkali cellulose is prepared. The preparation of alkali cellulose is very important to the overall process and the quality of the final product. The uniformity in the alkalization is one of the controlling factors for achieving uniformly substituted water soluble Methyl Cellulose. 5 kg. cellulose powder is charged in the 250 ltr. capacity S S - 316 L pressure reactor provided with mechanical seal, agitator, heating & cooling system, solid charging port, sampling point, addition vessel, liquid Methyl Chloride charging line, pressure gauge, digital temperature indicator, distillation system with collection / storage vessels. The cellulose powder in turn is reacted with 50 % Caustic Lye, which is prepared separately by dissolving 6 kg. Caustic Flakes in 6 Ltr. D M Water. The prepared 50% Caustic Lye is added at 15 -25°C under Nitrogen atmosphere & efficient stirring for 2 - 4 hrs. The quantities used should be in certain ratio. The weight ratio of Cellulose: Caustic: Water should be 1:1.2:1.2.
Step 2:
The reactor is cooled to 7 - 10°C & liquid Methyl Chloride (fresh / recovered / blend of both) is charged at 4 - 5 kg. / cm pressure. The temperature of the reactor is gradually increased to 45 - 55°C under the stirring. The methylation is continued for 16-20 hrs. at 10 - 14 kg. / cm2 pressure. The Methyl Chloride used in the process acts both as reactant and solvent in the reaction. The liquid Methyl Chloride should be in the weight ratio of 15-20 times of the cellulose powder taken.

Step 3:
After the completion of methylation, the excess of the Methyl Chloride is recovered by carrying out the distillation under pressure. The recovered Methyl Chloride is stored under pressure at room temperature in 200 ltr. S S 316 L storage vessel.
Step 4:
The Crude product is slurried in hot water (> 90°C) & centrifuged using SS - 316 basket type centrifuge. The washings are also given simultaneously using the hot water in order to remove the Sodium Chloride. Thus, the final product does not contain more than 0.5 % Chloride content, which is the requirement of the pharmaceutical grade product.
Step 5:
The wet cake is then taken out and dried at 90 - 105°C using the air circulating dryer.
Step 6:
The dried product is Finally pulverized & sieved.
The final product has aMethoxy substitution 28 - 32%, Chloride content <0.5%, 99 ±
1% Cold water solubility, Viscosity of 2% solution 5-15 cps and Solution clarity 10
-15NTU.
The above mentioned process efficiently utilizes the recovered Methyl chloride in the subsequent batches. The process will form a by-product Dimethyl ether but this particular process restricts the formation of Dimethyl ether to not more than 3 % per cycle of Methyl Chloride used in the methylation.
Over & above, the process of manufacturing Methyl Cellulose in accordance with the present invention provides an easy process to operate at this scale since most of the process steps are carried out in the same reactor system. The following examples given herein will substantiate our claims.
Example - 1
5.0 kg cellulose powder is reacted with 6.0 kg caustic dissolved in 6 Lit. DM Water at 20 ± 2°C under nitrogen atmosphere and efficient stirring. The total reaction time including the addition of caustic solution is kept in between 2-4 hrs. The reactor is further cooled to 7 - 10°C and 75 kg liquid Methyl Chloride is transferred at 4 - 5 kg / cm 2 pressure and methylation is carried out for 20 hrs at 50°C and 12.5 kg / /cm 2 pressure. The excess methyl chloride is recovered by carrying out the distillation under pressure and stored for the recycling / reuse in the process. The recovered Methyl Chloride contains less than 3 % Dimethyl ether. The crude product is slurried in 80 - 100 lit. hot water (> 90°C) and immediately centrifuged under the hot conditions including the washings. The wet product is dried in the air circulating dryer at 90 - 105 C followed by pulverization and sieving of the product

Example - 2
5.0 kg cellulose powder is reacted with 6.0 kg caustic dissolved in 6 Lit. D M Water at 23 ± 2°C under nitrogen atmosphere and efficient stirring. The total reaction time including the addition of caustic solution is kept in between 2-4 hrs. The reactor is further cooled to 7 - 10°C and 100 kg liquid methyl chloride is transferred at 4 - 5 kg /Cm2 pressure and methylation is carried out for 16 hrs at 55°C and 14 kg / /cm pressure. The excess Methyl Chloride is recovered by carrying out the distillation under pressure and stored for the recycling / reuse in the process. The recovered Methyl Chloride contains less than 3% Dimethyl ether. The crude product is slurried in 80 - 100 lit. hot water (> 90°C) and immediately centrifuged under the hot conditions including the washings. The wet product is dried in the air circulating dryer at 90 - 105°C followed by pulverization and sieving of the product.
Example - 3
5.0 kg cellulose powder is reacted with 6.0 kg caustic dissolved in 6 Lit. D M Water at 17 ± 2°C under nitrogen atmosphere and efficient stirring. The total reaction time including the addition of caustic solution is kept in between 2-4 hrs. The reactor is further cooled to 7 - 10°C and 80 kg recovered liquid methyl chloride is transferred at 4 - 5 kg / cm pressure and methylation is carried out for 20 hrs at 45 - 50 C and 10 -12 kg / cm pressure. The excess methyl chloride is recovered by carrying out the distillation under pressure and stored for the recycling / reuse in the process. The recovered methyl chloride contains less than 5% Dimethyl ether. The crude product is slurried in 80-100 lit. hot water (> 90°C) and immediately centrifuged under the hot conditions including the washings. The wet product is dried in the air circulating dryer at 90 - 105°C followed by pulverization and sieving of the product.
Example - 4
5.0 kg cellulose powder is reacted with 6.0 kg caustic dissolved in 6 Lit. D M Water at 17 ± 2°C under nitrogen atmosphere and efficient stirring. The total reaction time including the addition of caustic solution is kept in between 2-4 hrs. The reactor is further cooled to 7 - 10°C and 100 kg liquid methyl chloride (80 kg recovered + 20 kg fresh) is transferred at 4 - 5 kg / cm2 pressure and methylation is carried out for 20 hrs at 45 - 50°C and 10 - 12 kg / /cm 2 pressure. The excess methyl chloride is recovered by carrying out the distillation under pressure and stored for the recycling / reuse in the process. The recovered methyl chloride contains less than 5% Dimethyl ether. The crude product is slurried in 80 - 100 lit. hot water (> 90°C) and immediately centrifuged under the hot conditions including the washings. The wet product is dried in the air circulating dryer at 90 - 105°C followed by pulverization and sieving of the product.
The product obtained in all the examples shows Methoxy substitution 28 - 32%, chloride content <0.5%, 99 ± 1% Cold water solubility, Viscosity of 2% solution 5 -15 cps and Solution clarity 10-15 NTU.

We Claim:
1. An improved process for manufacturing cold water soluble Methyl Cellulose
comprising:
the step of Alkali Cellulose formation by reacting Cellulose powder with
Caustic Lye under inert atmosphere and efficient stirring;
the step of charging liquid Methyl Chloride in a pre-cooled reactor;
the step of reacting the Alkali Cellulose mass with the charged liquid
Methyl Chloride;
the step of recovering excess liquid Methyl Chloride for recycling the
same in the process;
the step of slurring the crude product in hot water having minimum 90 °C
temperature,
the step of centrifuging the slurry with simultaneous washings with hot
water having minimum 90 °C temperature;
the step of drying the wet cake; and
the steps of pulverizing and sieving the dry Methyl Cellulose.
2. A process as per Claim - 1, wherein Dimethyl Ether formation as a by-product is restricted to < 3 % per cycle of liquid Methyl Chloride used in the process.
3. A process as per Claim - 1, wherein the weight ratio of Cellulose:Caustic:Water is 1:1.2:1.2.
4. A process as per Claim - 1, wherein the Alkali Cellulose is prepared by the reaction of Cellulose powder and Caustic Lye at 15-25°C under inert atmosphere using Nitrogen.
5. A process as per Claim - 1, wherein the charging of liquid Methyl Chloride is carried out in the pre-cooled reactor below 10°C at pressure 4-5 kg/cm2.
6. A process as per Claim - 5, wherein the weight of liquid Methyl Chloride charged per cycle in the pre-cooled reactor is 15-20 times of that of the Cellulose Powder used in each cycle.
7. A process as per Claim - 1, wherein the methylation is carried out at 50 +/- 5 °C for 16-20 hours with reactor pressure 10 -14 kg/cm2.
8. A process as per Claim - 1, wherein the wet cake is dried in air-circulating dryer at 90-105 °C followed by the operations of pulverization and sieving.
9. A process as per Claim - 1, wherein the Methyl Cellulose manufactured has the following properties:

Methoxy substitution 28-32%, cold water solubility 99±1%, Chloride content less than 0.5 %, 2% aqueous solution viscosity 5- 15cps, Solution clarity 10-15 NTU and suitable for tablet coating.