DESC:FIELD OF THE INVENTION
The present disclosure relates to a method and apparatus for removal of at least 70% of hemicellulose impurity from spin bath solutions, such as spin bath solutions resulting from the production of cellulose products. Specifically, the disclosure relates to removal of at least 70% of hemicellulose impurity a spin bath N-Methyl- Morpholine N-Oxide (NMMO) solution.

BACKGROUND
Cellulosics or Cellulosic fibers are versatile and high-quality fibers, commonly obtained from natural cellulose by N-Methyl-Morpholine N-Oxide (NMMO) spinning process. Cellulosic fibers produced using such a process are also known as lyocell fibers. A conventional method of producing lyocell fibers includes following four steps: mixing, dissolving, spinning, and washing. NMMO is used in the production of lyocell fibres to dissolve cellulose from pulp resulting in formation of cellulose dope. The cellulose dope is spun into cellulosic fibers leaving behind a spent NMMO solution. During spinning, various
impurities associated with the cellulose dope leach out in the spent NMMO solution. For the economy of the process, spent NMMO solution (referred hereinafter as spin bath NMMO solution), is recovered and recycled after purifying it.

The process of purification of the spin bath NMMO solution includes removing impurities derived from pulp, other raw materials used in the process, impurities leached out from metallic equipments, and/or impurities that may have been formed by degradation reactions. The impurities frequently include inorganic cations and anions, hemicellulosic impurities obtained from the pulp and degraded cellulosic impurities. The known purification processes employ a combination of a conventional filter that removes any suspended particles from the spin bath NMMO solution along with one or more ion- exchange resin columns to remove ionic impurities. However, hemicellulosic impurities being soluble in the NMMO solution are not removed efficiently in such processes. Further, presence of hemicellulosic impurities in the spin bath NMMO solution reduces the efficiency of the ion exchange resins to remove ionic impurities.

Recycling of the spin bath NMMO solution containing hemicellulosic impurities for preparing cellulosic fibers may affect the manufacture and the quality of the fibers. For example, increase in hemicellulose beyond certain concentration may affect cellulose dissolution. Thus, there is a need for an efficient process for purification of the spin bath NMMO solution to efficiently remove soluble as well as the insoluble impurities.

BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 depicts a block diagram of an apparatus (100) for removal of hemicellulose impurities from a spin bath NMMO solution according to an embodiment of the present disclosure.
Fig. 2 depicts a block diagram of the apparatus (200) in accordance with another embodiment of the present disclosure.

SUMMARY OF THE INVENTION
According to an embodiment of the present invention, there is provided a method for removal of at least 70% of hemicellulose impurity from a spin bath N-Methyl-Morpholine N-Oxide (NMMO). The method comprises contacting the spin bath NMMO solution with ¬an activated granular carbonaceous material to filter the solution and then contacting the filtered solution with at least one ion-exchange resin.

According to another embodiment of the present invention, there is provided an apparatus for removal of at least 70% of hemicellulose impurity from a spin bath N-Methyl-Morpholine N-Oxide (NMMO) solution. The apparatus comprises the following components in sequence:
a. an inlet for receiving the feed of spin bath NMMO solution;
b. a bed of activated granular carbonaceous material for filtering the solution;
c. at least one ion-exchange resin column; and
d. an outlet for dispensing the NMMO solution.

DETAILED DESCRIPTION OF THE INVENTION
According to an embodiment of the present invention, the activated granular carbonaceous material used in the method for removal of at least 70% of hemicellulose impurity from a spin bath NMMO is preferably granular activated carbon. According to another embodiment of the present invention, the activated granular carbonaceous material in the apparatus is granular activated carbon. Ideally, the activated granular carbonaceous material has an iodine number of at least 750 mg/g. The ion-exchange resin used in the present invention can be an anion exchange resin or a cation exchange resin or both.

Preferably, the filtered solution is contacted with the ion-exchange resin until the electrical conductivity of the solution emerging from the resin reaches 15 µS/cm. Preferably, the spin bath NMMO solution is pre-filtered prior to contacting the solution with the carbonaceous material by placing a pre-filtration unit preceding the inlet. Preferably, the flow rate of the feed entering the inlet is maintained at 80 to 150 mL/hr the using a flow rate maintaining device such as a pump.

In Fig 1, an apparatus (100) for purification of a spin bath NMMO solution is disclosed. The apparatus (100) comprises an inlet (102) for receiving a feed of spin bath NMMO solution, an activated granular carbonaceous material, e.g., Granular Activated Carbon (GAC) bed (104), at least one ion-exchange resin column (106), and an outlet (108) for releasing a purified spin bath NMMO solution. The activated granular carbonaceous material bed (104) adsorbs hemicellulosic and other impurities from the spin bath solution. In accordance with an embodiment, the bed (104) is a column containing GAC. Preferably, the column is a glass column.
The ion-exchange resin column (106) includes at least one anion exchange resin columns and/or at least one cation exchange resin columns. In accordance with an embodiment, the ion-exchange resin column (106) includes one anion exchange resin column and one cation exchange resin column. Anion exchange resin can be strongly basic in nature whereas cation exchange resin can be strongly acidic in nature. Both resins are preferably based on styrene-divinylbenzene copolymer and are macroporous in nature.

Once the electrical conductivity of the purified spin bath NMMO solution coming out of the outlet (108) crosses 15 µS/cm (micro Siemens per centimetre) the system (100) is considered exhausted and may be regenerated.

The activated granular carbonaceous material bed (104) can be regenerated chemically by removing the adsorbed hemicellulose. In accordance with an embodiment, the bed (104) is regenerated by washing it with water and then treating it with a regenerant. Examples of the regenerant include but are not limited to lower alcohols or ketones such as methanol, ethanol or acetone. An ideal regenerant is ethanolic sodium hydroxide.

The ion-exchange resin column (106) can also be regenerated at suitable intervals by any of the conventionally known methods. It may be washed with water to remove any remaining spin bath NMMO solution. The cation exchange resin column is regenerated by treating washed column with 4-5% hydrochloric acid and the anion exchange resin column is regenerated by treating the washed column sequentially with 4-5% hydrochloric acid and 4-5% sodium hydroxide solutions.

Fig. 2 depicts a specific embodiment of the system (200), which comprises a pre-filtration unit (110), a peristaltic pump (112) for maintaining flow-rate placed between the activated granular carbonaceous material bed (104) and the pre-filtration unit (110) and a collection unit (114) placed between the bed (104) and the at least one ion-exchange resin column (106).

As depicted in Fig. 2, the pre-filtration unit (110) is placed before the activated granular carbonaceous material bed (104). The pre-filtration unit (110) removes any suspended particles such as sand, undissolved fibers, bacterial materials etc. from the spin bath NMMO solution. In an example, the pre-filtration unit (110) comprises a 1 µ (micron) Whatman filter paper (not shown in Fig.2) and a Buchner funnel (not shown in Fig. 2).

In accordance with an embodiment, the peristaltic pump (112) is a pre-calibrated peristaltic pump. The peristaltic pump (112) maintains a stable flow of the spin bath NMMO solution through the bed (104).

The collection unit (114) is used to collect a sample of the spin bath NMMO solution that has passed through the bed (104) and to analyse the sample for percentage hemicellulose reduction. The percentage hemicellulose reduction is the reduction in the hemicellulose content when the spin bath NMMO solution is passed through the bed (104).

It will be understood that based on the requirement, in certain embodiments, any one or more of the filtration unit (110), the peristaltic pump (112) and the collection unit (114) may be omitted. For example, for a commercial scale plant operation, the collection unit (114) is not required and the spin bath NMMO solution can directly pass to the ion-exchange resin column (106) from the bed (104).

A method for purification of a spin bath NMMO solution is also disclosed. The method comprises passing the spin bath NMMO solution through the bed of granular activated carbonaceous material (104) to obtain a filtered solution, and passing the filtered solution through the at least one ion-exchange resin column(s)(106) to obtain a purified spin bath NMMO solution.

The spin bath NMMO solution is fed into the bed (104) from the inlet (102). In accordance with an embodiment, the spin bath NMMO solution is fed into the bed (104) using the peristaltic pump (112). In accordance with an embodiment, the peristaltic pump (112) is pre-calibrated.

In accordance with an embodiment, the spin bath NMMO solution is passed through the bed (104) at a flow rate of 80 to 150 mL/hr.

In accordance with an embodiment, the method is continued till the conductivity of the purified spin bath NMMO solution crosses 15 µS/cm after which feed of the spin bath NMMO solution to the bed of granular activated carbonaceous material (104) is stopped and the bed (104) and the ion-exchange resin columns (106) are regenerated.

In accordance with an embodiment, the spin bath solution is passed through the filtration unit (110) before being passed through the bed of granular activated carbonaceous material (104) for removing any suspended particles from the spin bath solution.

The hemicellulose content of the filtered solution is at least 40% less than the inlet spin bath NMMO solution. The hemicellulose content of the spin bath solution emerging from the ion exchange column is at least 70% less than the inlet spin bath NMMO solution.

EXAMPLES
Details of a method for purification and regeneration of a spin bath NMMO solution according to the present disclosure are provided below.

Purification of a spin bath NMMO solution: A spin bath NMMO solution was first filtered by a filtration unit comprising a Whatman paper (1 micron) and a Buchner funnel to remove any suspended solids. The electrical conductivity and hemicellulose content of the filtered solution were measured. The filtered solution was then passed through a GAC bed using a pre-calibrated peristaltic pump. GAC filtered solution was collected in a collection unit such as a collection beaker from where it was passed through an anion exchange resin column. The solution from the anion exchange resin column was passed through a cation exchange resin column to obtain a purified spin bath NMMO solution. The purified spin bath NMMO solution was collected continuously and the electrical conductivity was measured at different time intervals.

Regeneration of the GAC bed and the ion-exchange resin columns: Electrical conductivity of the spin bath NMMO solution collected from the outlet was measured at different time intervals. Once the outlet conductivity crossed 15 µS/cm, the feed to the columns was stopped and the GAC bed and the ion-exchange resin columns were regenerated. The GAC bed was washed with water and then regenerated with an ethanolic sodium hydroxide solution. The cation exchange resin column was washed with water and then regenerated with 4-5% hydrochloric acid solution. The anion exchange resin column was washed with water and then regenerated by a sequential treatment with 4-5% hydrochloric acid and sodium hydroxide solutions.

Example 1:
Example 1 provides an illustration of a method for removal of at least 70% of hemicellulose impurity from a spin bath NMMO solution according to the present disclosure and a comparison of the efficiency of the method according to the present disclosure (experimental method) versus a conventional method for purification of spin bath NMMO solution.

A GAC bed was prepared by taking 40 to 50 ml of fresh GAC in a glass column. A spin bath NMMO solution containing about 20% NMMO was obtained after the spinning of lyocell fibers. The spin bath NMMO solution was filtered through a Whatman filter paper (1µm) placed on a Buchner funnel. After filtration, the spin bath NMMO solution was passed through the GAC bed at a flow rate of 80-150 mL/hr. 2-3 L of the solution was passed through GAC bed and was collected in a collection beaker. The GAC filtered solution was then passed through a strongly basic styrene-divinyl benzene based resin with quaternary amine as functional group commercially available as Lewatit S6368 which was used as the anion exchange resin in this case followed by a strongly acidic styrene-divinyl benzene resin with sulphonic acid as a functional group commercially available under the tradename Lewatit S2568 which was used as the cation exchange resin. The electrical conductivity of the solution from the outlet of the cation exchange resin column was measured at different intervals. The purification was stopped once the electrical conductivity of the solution from the outlet of the cation exchange resin columns was equal to or more than 15 µS/cm.

The experimental method was compared with a conventional method where spin bath NMMO solution is pre-filtered using 1 micron Whatman paper and then directly passed through the ion-exchange resin columns without any GAC treatment.

Experimental Results: Table 1 and 2 demonstrate the improved efficiency of the experimental method of the present disclosure over the conventional method of purification of spin bath NMMO solution. Table 1 and 2 further provides a comparison of percentage hemicellulose reduction obtained in the two methods.

Table 1: Comparison of volume of spin bath NMMO solution (Spin Bath Feed) that could be passed through 100ml ion-exchange resin column and hemicellulose content of the solution obtained after treatment with ion-exchange resin.

Sample
Code

Hemi-cellulose
(gpl)

Turbidity
(NTU)

Color - Yellowness index (YI)
Volume of solution that could be passed through 100ml ion-exchange resin column Hemi-cellulose
content of solution obtained after treatment with ion- exchange resin (gpl)
Spin Bath
Feed
(Conve-ntional)

1 - 2

1.2-2

40-50

7 - 8L

0.4-0.5
SBF
treated with GAC (Exp -erimental)

0.4-0.7

0.7-0.9

20-25

10-12L

0.1-0.2

Table 2: Amount of spin bath NMMO solution (in Litre) passed through 40-50ml GAC bed vs. percentage hemicellulose reduction obtained after purification according to the experimental method of the invention of Example 1.

Amount (L) of spin bath

NMMO solution passed through

40-50 ml GAC bed

% Hemicellulose Reduction
0.3-0.5 80-90
0.9-1.1 70-75
1.3-1.5 60-65
1.9-2.1 55-60
2.3-2.5 50-55
2.9-3 40-45

Observations: It was observed that to reduce hemicellulose content of the spin bath NMMO solution by 40 -50%, 2-3 L of the solution can be passed through GAC bed as described in Example 1. Further, it was observed that when GAC filtered solution was passed through the ion-exchange resin column, the performance of the ion-exchange resin column was increased by 25-35%. This means that 25 – 35 % more spin bath NMMO solution could be passed through the resin column.

A purification according to the experimental method of Example 1 resulted in a percentage hemicellulose reduction of 75-85%, while a purification according to the conventional method without GAC treatment resulted in a percentage hemicellulose reduction of 50 - 60% only.

INDUSTRIAL APPLICABILITY
The present disclosure discloses a method and an apparatus for removal of at least 70% hemicellulose impurity from a spin bath NMMO solution.

It has been observed that the overall hemicellulose content of the spin bath NMMO solution is reduced and the efficiency of ion exchange resin is improved. The hemicellulose content reduces by at least 40% when the solution is passed through the bed of granular activated carbonaceous material. The use of the said bed increases the efficiency of ion exchange resin column by 25 - 35 %. The hemicellulose content was overall reduced by at least 80 % by using the purification method and apparatus described herein.
,CLAIMS:We claim:

1. A method for removal of at least 70% of hemicellulose impurity from a spin bath N-Methyl-Morpholine N-Oxide (NMMO) solution, the method comprising contacting the spin bath NMMO solution with ¬an activated granular carbonaceous material and then contacting the filtered solution with at least one ion-exchange resin.

2. The method as claimed in claim 1, wherein the activated granular carbonaceous material is granular activated carbon.

3. The method as claimed in claim 1, wherein the activated granular carbonaceous material has an iodine number of at least 750 mg/g.

4. The method as claimed in claim 1, wherein the ion-exchange resin is an anion exchange resin or a cation exchange resin or both.

5. The method as claimed in claim 1, wherein the solution is contacted with the ion-exchange resin until the electrical conductivity of the solution emerging from the resin reaches 15 µS/cm.

6. The method as claimed in claim 1, wherein the spin bath NMMO solution is pre-filtered prior to contacting the solution with the activated granular carbonaceous material.

7. An apparatus for removal of at least 70% of hemicellulose impurity from a spin bath N-Methyl-Morpholine N-Oxide (NMMO) solution comprising the following in sequence:
a. an inlet for receiving the feed of spin bath NMMO solution;
b. a bed of activated granular carbonaceous material for filtering the solution;
c. at least one ion-exchange resin column; and
d. an outlet for dispensing the NMMO solution.

8. The apparatus as claimed in claim 7, wherein the activated granular carbonaceous material is granular activated carbon.

9. The apparatus as claimed in claim 7, wherein the activated granular carbonaceous material has an iodine number of at least 750 mg/g.

10. The apparatus as claimed in claim 7, wherein the ion-exchange resin is an anion exchange resin or a cation exchange resin or both.

11. The apparatus as claimed in claim 7, wherein the flow rate of the feed entering the inlet is maintained at 80 to 150 mL/hr using a flow rate maintaining device.

12. The apparatus as claimed in claim 7, wherein the inlet is preceded by a pre-filtration unit.