FORM 2
THE PATENTS ACT, 1970 (39 OF 1970)
&
THE PATENT RULES, 2005
(As Amended by Patents Amendment Rules – 2006)

PROVISIONAL SPECIFICATION
(See Section 10 and Rule 13)
TITLE OF INVENTION:
A continuous process for xanthation of alkali cellulose and a system thereof.
APPLICANT:
Aditya Birla Science and Technology Company Private Limited, Aditya Birla Center, 2nd Floor, ‘C’ wing, S.K. Ahire Marg, Worli, Mumbai- 400025, Maharashtra, India.
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes this invention and the manner in which it is to be performed. 2

FIELD OF THE INVENTION: 5
[001] The present invention relates to a continuous process for xanthation of alkali cellulose and a system thereof. More particularly, the present invention relates to a process for xanthation of alkali cellulose during the production of viscose for cellulose fibre and a system thereof.
BACKGROUND OF THE INVENTION:
[002] Cellulosic fibre prepared from viscose is conventionally produced by disintegrating cellulose 10 pulp by mixing it with alkali, pressing the alkali cellulose slurry to get a cake which is depolymerized by heating and then reacting with carbon disulphide (CS2) to yield alkali cellulose xanthate. In this process, usually the alkali content, during mercerization of the cellulose pulp is 17 to 18%, the cellulose content in the alkali cellulose slurry is 5%, while the alkali cellulose cake obtained after pressing contains 33 to 34% cellulose and 16 to 17% alkali. De-polymerisation of 15 alkali cellulose involves heating in a rotary drum for 3 to 5 hours to yield alkali cellulose crumbs which is then followed by the xanthation step.
[003] Typically, the xanthation of alkali cellulose is carried out in a batch process. As typical illustration of such kind of process is shown in Figure 1, wherein a compartment / reactor is first fed with alkali cellulose crumbs and then evacuated. Thereafter, CS2 is added to the alkali cellulose 20 crumbs under vacuum. Under applied vacuum, CS2 is vaporized and then diffused to alkali cellulose crumbs to form a sticky mass of cellulose xanthate, which is then dissolved in 1 to 2% alkali to form a viscous solution, i.e. the viscose. The viscose is then ripened and extruded through a tiny spinneret to produce cellulosic fibre.
[004] The conventional xanthation batch process has many drawbacks. For instance, during the 25 mixing of alkali cellulose with CS2, the alkali cellulose crumbs tend to form lumps of varying sizes. Due to the formation of these lumps, the alkali cellulose is not thoroughly saturated with CS2 and instead envelops the lumps leaving the alkali cellulose within the lumps unreacted in its 3

core. The cellulose xanthate so produced dissolves very slowly and imperfectly and has undissolved particles. These undissolved particles cause clogging of filters which requires their 30 frequent cleaning as well as causes interruptions in the spinning process. If the undissolved cellulose escape during the filtration and gets spun along with the fibre, it weakens the filament and destroys the uniformity within the filament. The unreacted alkali cellulose does not dissolve in the viscose solution leaving undissolved particles therein.
[005] Some drawbacks of the batch process include the presence of interruptions which occur due 35 to discharging the complete batch, cleaning the reactor and filling it with the new batch. Moreover, there is also batch to batch variation in the product which is another drawback. Since the process is carried out under vacuum, it is difficult to make the process continuous, yet the vacuum is required before and during introduction of CS2 to the reactor vessel because CS2 is explosive in air or oxygen. 40
[006] Hence, there is a need for a continuous xanthation process that would solve some of the problems present in the prior art.
SUMMARY OF THE INVENTION
[007] According to an embodiment of the present invention, there is provided a continuous process for xanthation of alkali cellulose comprising the steps of a) preparing a solution of carbon 45 disulphide and an organic solvent; b) agitating the solution and the alkali cellulose in a reaction vessel to prepare a homogenous slurry; c) obtaining an alkali cellulose xanthate in a single xanthation step by stirring and heating the slurry for a pre-determined residence time; d) removing a pre-determined quantity of the alkali cellulose xanthate from the reaction vessel; and e) filtering the alkali cellulose xanthate of step d) to simultaneously obtain a residual organic solvent and an 50 alkali cellulose xanthate cake, wherein the residual organic solvent is recirculated back and added 4

to the solution in step a) and the alkali cellulose xanthate cake is shredded and dissolved in an alkali having a concentration of 1-3% (w/w) to obtain viscose.
[008] According to an embodiment of the present invention, there is provided a system for a continuous process for xanthation of alkali cellulose comprising: 55
- a compartment for preparing a solution of carbon disulphide and an organic solvent;
- a reaction vessel operably connected to the compartment for preparing an alkali cellulose xanthate, the reaction vessel including:

- a first inlet for receiving a pre-determined quantity of the solution;
- a second inlet for receiving a pre-determined quantity of the alkali cellulose; 60
- an agitating means to form a slurry from a mixture of the solution and alkali cellulose, wherein the slurry is heated and agitated for a pre-determined residence time to form alkali cellulose xanthate in a single xanthation step;
- an outlet for removing a pre-determined quantity of the alkali cellulose xanthate from the reaction vessel; 65
- a filtering means operably connected to the reaction vessel for obtaining a residual organic solvent and alkali cellulose xanthate cake wherein the residual organic solvent is recirculated back and added to the solution;
- a shredder operably connected to the filtering means for receiving and shredding the alkali cellulose xanthate cake; and 70
- a dissolution vessel connected to the shredder for dissolving the shredded alkali cellulose xanthate cake with an alkali to form viscose.
BRIEF DESCRIPTION OF THE DRAWINGS:
[009] Figure 1 depicts a flow chart showing the batch process for xanthation of alkali cellulose as stated in the prior art. 75 5

[010] Figure 2 illustrates a flow chart showing a continuous process for xanthation of alkali cellulose according to the embodiments of the present invention.
[011] Figure 3 is a schematic representation of a continuous process for xanthation of alkali cellulose of Figure 2, according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS: 80
[012] As set out in the claims, the present invention eliminates or reduces the aforementioned problems of the prior art by providing a continuous process for xanthation of alkali cellulose during the manufacturing of viscose. The present invention also provides a system for a continuous process for xanthation of alkali cellulose which is simpler than the system provided in the prior art. 85
[013] According to an embodiment of the present invention, as shown in Figure 2, pre-determined quantities of CS2 and an organic solvent respectively are introduced into a compartment to prepare a solution. Pre-determined quantity of the solution is removed from the compartment and introduced into a reaction vessel along with pre-determined quantity of alkali cellulose to form a slurry, at room temperature. The alkali cellulose is introduced into the reaction 90 vessel containing (6-8) % CS2 in an organic solvent (w/w) to make a slurry with alkali cellulose consistency of (15-25) %. In an embodiment, the slurry obtained is homogeneous and the cellulose fibres are well separated from each other without any lumps being formed.
[014] The reaction vessel is filled with the solution and alkali cellulose up to a pre-determined level to form a slurry which is then continuously stirred and heated at 50-80°C for a pre-95 determined residence time of 30 to 45 mins in order for alkali cellulose to react with CS2. The CS2 slowly diffuses from the solution to the alkali cellulose and reaction between CS2 and alkali cellulose commences to yield a yellow coloured product of alkali cellulose xanthate. The partial 6

de-polymerization i.e. pre-ageing is carried out to achieve the required viscosity of the final viscose. 100
[015] After the completion of the reaction, a pre-determined quantity of the alkali cellulose xanthate is discharged and filtered to obtain residual organic solvent and an alkali cellulose xanthate cake. The alkali cellulose xanthate cake is shredded to form alkali cellulose xanthate crumbs. The alkali cellulose xanthate crumbs are dissolved in 1-3% alkali to form a viscose solution containing 6-9% cellulose and 4-6% alkali. The viscose obtained from this process is 105 used for making cellulose fibre by passing the viscose through a tiny spinneret and regenerating the filaments in an acidic solution. Preferably, 95-99% of the filtration is completed using a press, and the remaining 1-5% residual organic solvent can be removed from cellulose xanthate through evacuation. In an embodiment, the press used may be a filter press, a hydraulic press, a drum press or any other press conventionally known. 110
[016] In an embodiment, the residual organic solvent is recirculated back in the process to the compartment. Since the organic solvent does not dissolve alkali and impurities or byproducts generated during the reaction and is immiscible with water, no further purification of the recycled organic solvent is required. In an embodiment, excess quantity of carbon disulphide, which is equal to the quantity of carbon disulphide consumed during process, is added at the first 115 step in order to maintain the pre-determined quantity of carbon disulphide in the solution prepared at the first step.
[017] In an embodiment, the organic solvent is one which is miscible with CS2 but immiscible with water and does not dissolve alkali. Preferably, the organic solvent is selected from hydrocarbons having carbon atoms 5-18 such as petroleum ether, wax, toluene, xylene, 120 dichloroethane, or the like. 7

[018] In an embodiment, the reaction vessel is a continuous stirred-tank reactor (CSTR). In an embodiment, the alkali cellulose is in the form of crumbs obtained after mercerization and partial de-polymerization. Preferably, the solution prepared is a stock solution and the concentration of CS2 in the organic solution is in the range of (5-10) %. 125
[019] According to an embodiment of the present invention, there is provided a system for a continuous xanthation of alkali cellulose. Figure 3 depicts a schematic representation of the system having a compartment (100) for preparing a solution (4) of carbon disulphide (CS2) (2) and an organic solvent (3). In a reaction vessel (101) that is operably connected to the compartment (100), a pre-determined quantity of the solution (4) is added through an inlet and a pre-determined quantity 130 of the alkali cellulose (1) is added from another inlet to form a slurry. The slurry comprises (6-8) % CS2, (15-25) % alkali cellulose and (60-80) % organic solvent. The reaction vessel is filled with the solution and the alkali cellulose up to a pre-determined level. The slurry is continuously agitated using an agitating means (102) and heated at (50-80) °C, preferably 60°C to form a homogenous slurry. The alkali cellulose in the suspension reacts with CS2 to form alkali cellulose xanthate 135 in a pre-determined residence time of 30 to 45 mins. A pre-determined quantity of the said alkali cellulose xanthate (5) is removed continuously from the outlet of the reaction vessel (101) in such a manner that the alkali cellulose is exposed to CS2 for appropriate and uniform time for the reaction to be completed. The resulting alkali cellulose xanthate (5) is filtered using a filter press (103) to obtain a residual organic solvent (6) and an alkali cellulose xanthate cake (7). The 140 said residual organic solvent (6) is recirculated back and added to the solution in the compartment (100) and used for further xanthation with appropriate addition of CS2 without further purification. The alkali cellulose xanthate cake is transferred to a shredder (104) and the shredded cake of alkali cellulose xanthate (8) is thereafter transferred to a dissolution vessel (105) in which it is mixed with alkali (9) and stirred to yield viscose (10). 145 8

[020] In the present invention, since CS2 is dissolved in an organic solvent hence there is no need to create vacuum thereby avoiding the possibility of any explosion during the process. Also, by dissolving CS2 in an organic solvent the availability of CS2 for alkali cellulose is increased resulting in formation of a homogenous slurry thereby increasing the process speed and reducing the process time. 150
[021] The reaction between CS2 and alkali cellulose in the organic medium is quite slow as compared to the reaction according to conventional method wherein the reaction between CS2 and alkali cellulose is achieved through the diffusion of CS2 vapor into solid alkali cellulose. As the reaction between CS2 and alkali cellulose in an organic medium is comparatively slow, it can be controlled and optimized by varying temperature, time and CS2 concentration in the organic 155 solvent to result in a viscose solution having the desired properties. The viscose solution obtained using this method contains no lumps and very few undissolved particles as compared to that obtained from the conventional method. The continuous feeding of the solution of organic solvent and CS2 along with alkali cellulose into the reaction vessel and the continuous discharge of the resulting alkali cellulose xanthate is carried out in such a manner that all the alkali cellulose is 160 exposed for uniform time to CS2 for the reaction, so the resulting cellulose xanthate possesses uniform properties. Also, consumption of CS2 in the present process is limited i.e. the present invention involves addition of slight excess CS2 for the xanthation reaction of which only 27 to 30% CS2 with respect to cellulose is consumed in the xanthation reaction while conventional methods involve the use of more than 32% CS2. 165
[022] Preferably, the viscose obtained by the method of the present invention contains 6-10% cellulose, 4-6% alkali with viscosity of 4000-7000 centi Poise (cP) and filterability index of less than 200.
[023] The following experimental example is illustrative of the invention but not limitative of the 9

scope thereof: 170
Example 1: Xanthation of alkali cellulose using conventional method
[024] 77 g of cellulose was mixed with 1.3 kg aqueous alkali solution (18% NaOH, w/w), followed by the addition of 1% surfactant and 10 ppm MnSO4 with respect to cellulose to make a slurry having 5% cellulose consistency. The slurry was mercerized for 15 mins at 50°C and then excess liquid was squeezed out through pressing under a hydraulic press to get the alkali cellulose cake 175 comprising of 34-35% cellulose and 15-16% NaOH by weight. The alkali cellulose cake was shredded in a mixer-grinder. The shredded alkali cellulose was transferred into a glass vessel and heated under rotation at 50°C for 3h to undergo de-polymerization i.e. pre-ageing.
[025] 100 g of depolymerized alkali cellulose was kept in a 500 mL of flask attached to a rotavapor. The alkali cellulose was cooled to 30°C and the flask was evacuated up to the vacuum of 2 torr. 180 10 mL carbon disulphide (CS2) was added to the flask under vacuum. The flask was rotated in rotatory evaporator at 30°C for 45 min to complete the reaction between alkali cellulose and CS2 to form sodium cellulose xanthate. The resulting cellulose xanthate was added to 2% alkali cellulose at 20°C and stirred for 4h to get the viscose solution with 9% cellulose and 5.5% alkali. The characteristics of the viscose solution is shown in Table 1. 185
Example 2: Xanthation of alkali cellulose in organic media
[026] 77 g of cellulose pulp was mixed with 1.3 kg aqueous alkali solution (18% NaOH, w/w), followed by the addition of 1% surfactant and 10 ppm MnSO4 with respect to cellulose to make a slurry having 5% cellulose consistency. The slurry was mercerized for 15 mins at 50°C and then excess liquid was squeezed out through pressing under a hydraulic press to get the alkali cellulose 190 cake comprising 34-35% cellulose and 15-16% NaOH by weight. The alkali cellulose cake was shredded in a mixer-grinder. The shredded alkali cellulose was transferred into a glass vessel and 10

heated under rotation at 50°C for 1h to undergo partial depolymerization i.e. pre-ageing.
[027] 40 g of CS2 and 460 g of petroleum ether (B.P. 100-120°C) was added to a jacketed vessel equipped with stirrer and water/oil bath circulation and mixed well. The temperature of the solution 195 was raised to 60°C and at this temperature, 100 g of depolymerized alkali cellulose was added. The reaction mixture was stirred for 45 min at 60°C to form a yellow-orange coloured alkali cellulose xanthate. The resulting cellulose xanthate was filtered using filter press and shredded. The residual petroleum ether solvent was removed by keeping the xanthate crumbs under vacuum for 5-10 min. The shredded cellulose xanthate was added to 2% aqueous alkali at 20°C and kept 200 under stirring for 2h to get the viscose solution having 9% cellulose and 5.5% alkali. The resulting viscose solution was found to be very much comparable to the viscose prepared using conventional method. A comparative analysis of the viscose is shown in Table 1.
Example 3: Continuous xanthation of alkali cellulose in organic media
[028] 385 g of cellulose was added to 6.5 kg aqueous alkali solution (18% NaOH, w/w) followed 205 by the addition of 1% surfactant and 10 ppm MnSO4 with respect to cellulose to make a slurry having 5% cellulose consistency. The slurry was mercerized for 15 min at 50°C and then excess liquid was squeezed out through pressing under a hydraulic press to get the alkali cellulose cake with composition 34-35% cellulose and 15-16% NaOH by weight. The alkali cellulose cake was shredded in a mixer-grinder. The shredded alkali cellulose was transferred in a glass vessel and 210 heated under rotation at 50°C for 1h to undergo the partial depolarization to get 1 kg of depolymerized alkali cellulose for continuous xanthation reaction.
[029] The xanthation process is made continuous using continuous stirred-tank reactor (CSTR) equipped with stirrer and water/oil bath circulation. The CS2, petroleum ether (B.P. 100-120°C), and depolymerized alkali cellulose is mixed to form suspension which is comprised of 6.4% CS2, 215 11

16.8% alkali cellulose, and 76.8% petroleum ether. This suspension is feed continuously to CSTR with a flow rate 125 g per minute using plunger type metering pump. The suspension is stirred at 60°C to react alkali cellulose in suspension with CS2 to form cellulose xanthate. The reaction mass of 5000 g and residence time of 40 min maintained in the CSTR to achieve the required degree of xanthation of alkali cellulose. The resulting cellulose xanthate suspension is removed continuously 220 from the reactor using peristaltic pump with the rate of 125 g per minute with slurry consistency of 5.7 to 5.9%. The cellulose xanthate slurry is filtered continuously to get cellulose xanthate cake and the filtered organic solvent is recycled and used for further xanthation with appropriate addition of CS2 without further purification.
[030] The xanthate cake is shredded and dissolved in 2% aqueous alkali at 20°C with stirring for 225 60 min to get the viscose solution. The resulting viscose solution was found to be comparable to the viscose prepared using conventional method. A comparative analysis of the viscose is shown in Table 1.
Table 1 - Comparative analysis of viscose properties
230 Viscose Pre-ageing time Cellulose viscosity after presaging % CS2 consumed % CS2 in viscose Ageing time Gamma No Viscosity of viscose at 20oC Kw
Example 1 3h 6.0 cP 38 % 34.5 % 4h 31.2 7760 cP 113.1
Example 2 1h 8.1 cP 30 % 29.5 % 2h 33.4 7880 cP 176.3
Example 3 1h 8.3 cP 30 % 29.6 % 2h 33.6 7840 cP 168.5

[031] As is evident from Table 1, the filterability index (Kw) does not exceed 200 in the method of the present invention. A filterability index of below 200 is desirable, and the conventional method is comparable to the method of the present invention in this respect. Also, the viscosity of the viscose obtained in Examples 2 and 3 is comparable to that obtained by the conventional 235
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method. Further, the time of pre-aging and aging were significantly reduced in the process of Examples 2 and 3 as compared to the conventional method. Additionally, the consumption of CS2 was lower in the process of Examples 2 and 3 as compared to the conventional method making the method of the invention more economical.
[032] The foregoing description of specific embodiments of the present invention has been 240 presented for purposes of description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obvious modifications and variations are possible in light of the above teaching.
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WE CLAIM: 245
1. A continuous process for xanthation of alkali cellulose comprising the steps of:
a) preparing a solution of carbon disulphide and an organic solvent;
b) agitating the solution and the alkali cellulose in a reaction vessel to prepare a homogenous slurry;
c) obtaining an alkali cellulose xanthate in a single xanthation step by stirring and heating the 250 slurry for a pre-determined residence time;
d) removing a pre-determined quantity of the alkali cellulose xanthate from the reaction vessel;
e) filtering the alkali cellulose xanthate of step d) to simultaneously obtain a residual organic solvent and an alkali cellulose xanthate cake, wherein the residual organic solvent is 255 recirculated back and added to the solution in step a) and the alkali cellulose xanthate cake is shredded and dissolved in an alkali having a concentration of 1-3% (w/w) to obtain viscose.
2. The process as claimed in claim 1, wherein the reaction vessel is a continuous stirred-tank reactor. 260
3. The process as claimed in claim 1, wherein the slurry is heated up to a temperature of (50-80)oC during the residence time of 30-45 minutes.
4. The process as claimed in claim 1, wherein the organic solvent is selected from hydrocarbons having carbon atoms 5-18 such as petroleum ether, wax, toluene, xylene, dichloroethane, or the like. 265
5. The process as claimed in claim 1, wherein the pre-determined quantity of the alkali cellulose xanthate removed from the process at step d) is equal to the amount of solution and alkali cellulose filled in the reaction vessel to form a slurry at step b) in order to maintain the reaction volume in the reaction vessel.
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6. The process as claimed in claim 1, wherein the viscose obtained at step f) has 6-10% cellulose, 270 4-6% alkali with viscosity of 4000-7000 centi Poise and filterability index of less than 200.
7. A system for a continuous process for xanthation of alkali cellulose comprising:
- a compartment for preparing a solution of carbon disulphide and an organic solvent;
- a reaction vessel operably connected to the compartment for preparing an alkali cellulose xanthate, the reaction vessel including: 275
- a first inlet for receiving a pre-determined quantity of the solution;
- a second inlet for receiving a pre-determined quantity of the alkali cellulose;
- an agitating means to form a slurry from a mixture of the solution and alkali cellulose, wherein the slurry is heated and agitated for a pre-determined residence time to form alkali cellulose xanthate in a single xanthation step; 280
- an outlet for removing a pre-determined quantity of the alkali cellulose xanthate from the reaction vessel;
- a filtering means operably connected to the reaction vessel for obtaining a residual organic solvent and alkali cellulose xanthate cake wherein the residual organic solvent is recirculated back and added to the solution; 285
- a shredder operably connected to the filtering means for receiving and shredding the alkali cellulose xanthate cake; and
- a dissolution vessel connected to the shredder for dissolving the shredded alkali cellulose xanthate cake with an alkali to form viscose.
8. The system as claimed in claim 7, wherein the slurry is heated up to a temperature of (50-80)°C 290 during the residence time of 30-45 minutes.
9. The system as claimed in claim 7, wherein the organic solvent is selected from hydrocarbons having carbon atoms 5-18 such as petroleum ether, wax, toluene, xylene, dichloroethane, or the like.
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10. The system as claimed in claim 7, wherein the pre-determined quantity of the alkali cellulose 295 xanthate removed from the reaction vessel is equal to the amount of solution and alkali cellulose filled in the reaction vessel to form a slurry in order to maintain the reaction volume in the reaction vessel.
Dated this 25th day of October, 2018 300
For Aditya Birla Science and Technology Company Private Limited.