Indian Patents. 233992:A PROCESS FOR RECOVERY OF LIGNIN FROM BLACK LIQUOR

Title of Invention	A PROCESS FOR RECOVERY OF LIGNIN FROM BLACK LIQUOR
Abstract	N/A

Full Text	THE PATENTS ACT. 1970 COMPLETE SPECIFICATION SECTION 10 TITLE "A lignin recovery system and to a process therefor' APPLICANT JAI PRAKASH SEMWAL, an Indian National of Chandera, P.B.No.50, Balaghat Road, Gondia 441 601, Maharashtra, India. The following specification describes the nature of this invention. 16 AUG 2004 -2- FIELD OF INVENTION This invention relates to a lignin recovery system and to a process therefor. In particular, this invention relates to a system for treatment of black liquor discharged as an effluent from a pulp unit. BACKGROUND OF INVENTION It is generally known that black liquor generated from pulping of agricultural residues possesses a dark brown colour with a high BOD and COD content due to presence of lignin as a main component. A lignin is a polymat present in all plants which is a high molecular and low reactivity substance. Due to presence of large number of monomers lignin is difficult to degrade chemically or biologically. In conventional systems the black liquor is evaporated, incinerated and causticized to remove the organic lignin and recover the cooking chemicals by causticizing. Such a process is viable only with more than 60 TPD (Tonnes per day) plants and conventional raw materials like woods and bamboo etc. In case of raw materials like bagasse, wheat straw and rice straw with production of less than 60 TPD it is economically and technically unviable due to high silica content, high capital investment and high processing cost etc. -3- OBJECTS OF THE INVENTION An object of this invention is to propose a recovery system to recover lignin from black liquor and a process therefor. Another object of this invention is to propose a recover}' system to recover lignin from black liquor and a process therefor WHICH is simple and be used with paper mills having a capacity of 60 TPD and less. Still another object of this invention is to propose a recovery system to recover lignin from black liquor and a process therefor which has a low capital investment in comparison to that of the known art. Yet another object of this invention is to propose a recovery system to recover lignin from black liquor and a process therefor which has a low operational cost. A further object of this invention is to propose a recover system to recover lignin from black liquor and a process therefor which is efficient. Further objects and advantages of this invention will be more apparent from the ensuing description. description. At the outset of the description, which follows, it is to be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only an exemplary embodiment and without intending to imply a limitation on the teaching of the invention and nor to be taken restrictively. BRIEF DESCRIPTION OF INVENTION According to this invention there is provided a process for the recover}' of lignin from black liquor comprising in the steps of: a) mixing the black liquor with an acid so as to produce a flocculated slurry of precipitated lignin and black liquor, b) introducing the flocculated slurry into a filter bed containing a plurality of sand and gravel beds to cause a separation of the lignin, c) the filtrate from the filter bed being subjected to primary clarification with mill effluent. Further, according to this invention there is provided a system for the recovery of lignin from black liquor comprising : i) a mixer tame with a rotatable mixer for causing a mixing of black liquor and an acid, (ii) a flocculator for receiving the flocculated slurry from said mixer, (iii) a filter housing having a plurality of sand and gravel beds for receiving the slurry from the flocculator, (iv) a filtrate tank for receiving the filtrate from said filter housing. -5- In accordance with this invention the black liquor is treated with a mineral acid to enable the lignin to precipitate and retained in a flocculation chamber. The flocculated slurry is then transferred to filter beds to separate the lignin from suspension. A thick cake is formed on the filter bed which can be remove manually. The filtrate, which is very light in colour and has very low COD value in comparison to black liquor can be treated along with the other mill effluent. Both laboratory studies and pilot scale experiments have shown the process to be theoretically possible and practically viable. DESCRIPTION WITH REFERENCE TO DRAWINGS Further objects and advantages of this invention will be more apparent from the ensuing Description when read in conjunction with the accompanying drawing and wherein Fig. 1 shows the apparatus of the present invention. Referring to fig.l, the apparatus comprises a mixer tank 1 having a rotatable mixer la. And such as sulphuric acid from an acid tank 2 is introduced into mixer tank 1. Black liquor is pumped to mixer tank 1 through a pump 3. A mixing of black liquor with acid is caused in tank 1 and such that precipitation of lignin. -6- Mixer 1 has an outlet lb in flow communication with a flocculator 3. Preferably, the mixture of acid and black liquor is retained in the flocculating tank for ¾ to 1½ hours. The overflow from flocculating tank 3 is introduced into a filter bed 4 and the thick sludge of lignin is removed for suitable disposal, such as incineration in a boiler furnace after drying. Filter bed 4 comprises a plurality of sand and gravel beds to cause a separation of lignin. The period of filtration can be between 24 to 36 hours. The filtrate from filter 4 is fed to a filtrate tank 5 and then pumped by pump 6 to a clarifier for treatment with mill effluent. EXAMPLE 1 During trials filtrate was collected and tested for colour, BOB and COB. A comparison of black liquor and filtrate after treatment is given as under :- Particulars Unit Black liquor Filter water Benefits/removal Colour - Blackish Brown Straw Yellow Very good COD Ppm >70000 BOD Ppm 3000 600/700 75-80% -7- EXAMPLE 2 On a laboratory basis, one liter fresh and old black liquor was taken in a measuring cylinder and acidified to a pH of 3.5-3.8 to precipitate the lignin. The solution became very viscose and precipitates were tending to float and were not settling down. Hence removal of lignin by sedimentation process was rejected as a pilot trial option. To separate the precipitates from liquor a filter bed was designed which was able to filter the slurry in less than 12 hours. After 12 hours a thick mat of lignin was observed on the top of the filter bed and clear filtrate of straw yellow colour was collected separately, which was checked for its BOD and COD. The system was found to be working equally well for the black liquor i.e. fresh black liquor and black liquor stored in lagoons for 3 to 4 months. However, reduction in BOD and COD, was found to be more in stored black liquor nitrate. TABLE II Filtrate analysis Particulars Unit Filtrate New Black Liquor One Black Liquor filtrate COLOUR - DARK STRAW PALE STRAW COD - 6000 4500 BOD - 700-800 500-550 -8-WE CLAIM: 1. A process for the recovery of lignin from black liquor comprising in the steps of: a) mixing the black liquor with an acid so as to produce a flocculated slurry of precipitated lignin and black liquor, b) introducing the flocculated slurry into a filter bed containing a plurality of sand and gravel beds to cause a separation of the lignin, c) the filtrate from the filter bed being subjected to primary clarification with mill effluent. 2. A process as claimed in claim 1 wherein the pH of the mixture of black liquor and is reduced to pH 2-8 to 3. 3. A process as claimed in claim 1 wherein the acid is for example sulphuric acid. 4. A process as claimed In claim 1 wherein a filtration in the filter bed is carried out for 24 to 36 hours. 5. A process for the recovery of lignin from black liquor substantially as herein described and illustrated. -9- 6. A system for the recovery of lignin from black liquor comprising : a) a mixer tank with a rotatable mixer for causing a mixing of black liquor and an acid, b) a flocculator for receiving the flocculated slurry from said mixer, c) a filter housing having a plurality of sand and gravel beds for receiving the slurry from the flocculator, d) a filtrate tank for receiving the filtrate from said filter housing. 7. A system for the recovery of lignin from black liquor substantially as herein described and illustrated. N/A

Full Text

THE PATENTS ACT. 1970
COMPLETE
SPECIFICATION
SECTION 10
TITLE
"A lignin recovery system and to a process therefor'
APPLICANT
JAI PRAKASH SEMWAL, an Indian National of Chandera, P.B.No.50, Balaghat Road, Gondia 441 601, Maharashtra, India.
The following specification describes the nature of this invention.

16 AUG 2004

-2-
FIELD OF INVENTION
This invention relates to a lignin recovery system and to a process therefor. In particular, this invention relates to a system for treatment of black liquor discharged as an effluent from a pulp unit.
BACKGROUND OF INVENTION
It is generally known that black liquor generated from pulping of agricultural residues possesses a dark brown colour with a high BOD and COD content due to presence of lignin as a main component. A lignin is a polymat present in all plants which is a high molecular and low reactivity substance. Due to presence of large number of monomers lignin is difficult to degrade chemically or biologically.
In conventional systems the black liquor is evaporated, incinerated and causticized to remove the organic lignin and recover the cooking chemicals by causticizing. Such a process is viable only with more than 60 TPD (Tonnes per day) plants and conventional raw materials like woods and bamboo etc. In case of raw materials like bagasse, wheat straw and rice straw with production of less than 60 TPD it is economically and technically unviable due to high silica content, high capital investment and high processing cost etc.

-3-
OBJECTS OF THE INVENTION
An object of this invention is to propose a recovery system to recover lignin from black liquor and a process therefor.
Another object of this invention is to propose a recover}' system to recover lignin from black liquor and a process therefor WHICH is simple and be used with paper mills having a capacity of 60 TPD and less.
Still another object of this invention is to propose a recovery system to recover lignin from black liquor and a process therefor which has a low capital investment in comparison to that of the known art.
Yet another object of this invention is to propose a recovery system to recover lignin from black liquor and a process therefor which has a low operational cost.
A further object of this invention is to propose a recover system to recover lignin from black liquor and a process therefor which is efficient.
Further objects and advantages of this invention will be more apparent from the ensuing description.
description.

At the outset of the description, which follows, it is to be understood that the ensuing
description only illustrates a particular form of this invention. However, such a particular
form is only an exemplary embodiment and without intending to imply a limitation on the
teaching of the invention and nor to be taken restrictively.
BRIEF DESCRIPTION OF INVENTION
According to this invention there is provided a process for the recover}' of lignin from
black liquor comprising in the steps of:
a) mixing the black liquor with an acid so as to produce a flocculated slurry of precipitated lignin and black liquor,
b) introducing the flocculated slurry into a filter bed containing a plurality of sand and gravel beds to cause a separation of the lignin,
c) the filtrate from the filter bed being subjected to primary clarification with mill effluent.
Further, according to this invention there is provided a system for the recovery of lignin
from black liquor comprising :
i) a mixer tame with a rotatable mixer for causing a mixing of black liquor and an
acid,
(ii) a flocculator for receiving the flocculated slurry from said mixer,
(iii) a filter housing having a plurality of sand and gravel beds for receiving the slurry
from the flocculator,
(iv) a filtrate tank for receiving the filtrate from said filter housing.
-5-
In accordance with this invention the black liquor is treated with a mineral acid to enable the lignin to precipitate and retained in a flocculation chamber. The flocculated slurry is then transferred to filter beds to separate the lignin from suspension. A thick cake is formed on the filter bed which can be remove manually.
The filtrate, which is very light in colour and has very low COD value in comparison to
black liquor can be treated along with the other mill effluent. Both laboratory studies and
pilot scale experiments have shown the process to be theoretically possible and
practically viable.
DESCRIPTION WITH REFERENCE TO DRAWINGS
Further objects and advantages of this invention will be more apparent from the ensuing
Description when read in conjunction with the accompanying drawing and wherein
Fig. 1 shows the apparatus of the present invention.
Referring to fig.l, the apparatus comprises a mixer tank 1 having a rotatable mixer la. And such as sulphuric acid from an acid tank 2 is introduced into mixer tank 1. Black liquor is pumped to mixer tank 1 through a pump 3. A mixing of black liquor with
acid is caused in tank 1 and such that precipitation of lignin.

-6-
Mixer 1 has an outlet lb in flow communication with a flocculator 3. Preferably, the mixture of acid and black liquor is retained in the flocculating tank for ¾ to 1½ hours.
The overflow from flocculating tank 3 is introduced into a filter bed 4 and the thick sludge of lignin is removed for suitable disposal, such as incineration in a boiler furnace after drying. Filter bed 4 comprises a plurality of sand and gravel beds to cause a separation of lignin. The period of filtration can be between 24 to 36 hours.
The filtrate from filter 4 is fed to a filtrate tank 5 and then pumped by pump 6 to a clarifier for treatment with mill effluent.
EXAMPLE 1
During trials filtrate was collected and tested for colour, BOB and COB. A comparison of black liquor and filtrate after treatment is given as under :-

Particulars Unit Black liquor Filter water Benefits/removal
Colour - Blackish Brown Straw Yellow Very good
COD Ppm >70000 BOD Ppm 3000 600/700 75-80%

-7-
EXAMPLE 2
On a laboratory basis, one liter fresh and old black liquor was taken in a measuring cylinder and acidified to a pH of 3.5-3.8 to precipitate the lignin. The solution became very viscose and precipitates were tending to float and were not settling down. Hence removal of lignin by sedimentation process was rejected as a pilot trial option.
To separate the precipitates from liquor a filter bed was designed which was able to filter the slurry in less than 12 hours.
After 12 hours a thick mat of lignin was observed on the top of the filter bed and clear

filtrate of straw yellow colour was collected separately, which was checked for its BOD

and COD. The system was found to be working equally well for the black liquor i.e. fresh black liquor and black liquor stored in lagoons for 3 to 4 months. However, reduction in BOD and COD, was found to be more in stored black liquor nitrate.
TABLE II Filtrate analysis

Particulars Unit Filtrate New Black Liquor One Black Liquor filtrate
COLOUR - DARK STRAW PALE STRAW
COD - 6000 4500
BOD - 700-800 500-550

-8-WE CLAIM:
1. A process for the recovery of lignin from black liquor comprising in the steps of:
a) mixing the black liquor with an acid so as to produce a flocculated slurry of precipitated lignin and black liquor,
b) introducing the flocculated slurry into a filter bed containing a plurality of sand and gravel beds to cause a separation of the lignin,
c) the filtrate from the filter bed being subjected to primary clarification with mill effluent.

2. A process as claimed in claim 1 wherein the pH of the mixture of black liquor and is reduced to pH 2-8 to 3.
3. A process as claimed in claim 1 wherein the acid is for example sulphuric acid.
4. A process as claimed In claim 1 wherein a filtration in the filter bed is carried out for 24 to 36 hours.
5. A process for the recovery of lignin from black liquor substantially as herein described and illustrated.

-9-
6. A system for the recovery of lignin from black liquor comprising :
a) a mixer tank with a rotatable mixer for causing a mixing of black liquor and an acid,
b) a flocculator for receiving the flocculated slurry from said mixer,
c) a filter housing having a plurality of sand and gravel beds for receiving the slurry from the flocculator,
d) a filtrate tank for receiving the filtrate from said filter housing.

7. A system for the recovery of lignin from black liquor substantially as herein described and illustrated.

N/A

A PROCESS FOR RECOVERY OF LIGNIN FROM BLACK LIQUOR

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