CA1274628A - Pulp decolor process - Google Patents
Pulp decolor processInfo
- Publication number
- CA1274628A CA1274628A CA000512305A CA512305A CA1274628A CA 1274628 A CA1274628 A CA 1274628A CA 000512305 A CA000512305 A CA 000512305A CA 512305 A CA512305 A CA 512305A CA 1274628 A CA1274628 A CA 1274628A
- Authority
- CA
- Canada
- Prior art keywords
- waste water
- bodies
- color bodies
- contacting
- pulp
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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- Paper (AREA)
- Separation Of Suspended Particles By Flocculating Agents (AREA)
Abstract
PULP DECOLOR PROCESS
ABSTRACT OF THE DISCLOSURE
A process for the decolorization of alkaline pulp such as that derived from paper waste water wherein the waste water is contacted with a strong mineral acid, contacted with a coagulated agent and then the solid coagulum is separated and neutralized to liquify the color bodies in concentrated form.
ABSTRACT OF THE DISCLOSURE
A process for the decolorization of alkaline pulp such as that derived from paper waste water wherein the waste water is contacted with a strong mineral acid, contacted with a coagulated agent and then the solid coagulum is separated and neutralized to liquify the color bodies in concentrated form.
Description
7a~6~8 PULP DECOLOR PROCESS
S P E C I F I C A T I O N
This invention relates to the decolorization of pulp and paper waste waters, and more particularly to a process for the resource recovery of the organic materials removed by the decolorization process.
Pulp and paper waste waters have presented, for many years, a formidable waste treatment problem. For example, typical kraft pulp mills generate millions of gallons of waste water everyday containing suspended and colloidal solids made up chiefly of pulp fibers and color bodies, usually in the form of lignins and the products of the oxidation and thermal degradation of wood sugars. The latter waste causes the primary concern because of the high biological oxygen demand and non-aesthetic characteristics of such wastes if treated conventionally.
Various techniques have been proposed to remove the colloidal color bodies, suspended solids and associated high BOD. One technique has involved the addition of massive quantities of lime to the waste water from which pulp fibers and ligneous matter have been separated. The lime addition flocculates the color bodies and thereby reduces the initial waste water color of the waste stream by 80-90~ as well as significantly reducing the BOD. That technique has a significant disadvantage in that it involves high capital and operating costs. In addition, such waste water techniques do ~746X8 not allow for reCoYery of the pulp or lignatious material collected by the process. Finally, the quantities of lime employed pose very significant problems in lime handling, sludge removal and ultimate waste water quality.
It has also been proposed to contact sush waste waters with an ion exchange resin which is capable of absorbing the lignins and their derivatives. Ion exchange resins for that purpose have generally been highly cross linked, hydrophilic acrylic copolymers which absorb the organic components by means of Van der Waal's forces.
one of the primary disadvantages of the ion exchange technique is that the resin removes free chloride ions as well as the color bodies. When the ion exchange rQsin is regenerated, the chloride ions thus released have a tendency to build up in the system to create high chloride levels. That method is also extremely costly.
It is accordingly an object of an aspect of the present invention to provide a process of decolorizing pulp and paper waste waters containing color bodies which overcomes the foregoing disadvantages.
It is an object of an aspect of the present invention to provide a process for the decolorization of alkaline pulp and paper waste waters containing as color bodies lignins and derivatives thereof which can be carried out at low cost without substantially capital outlays and which is capable of substantially complete recovery o~ wasted pulp and lignatious materials.
These and other objects of the present invention will appear more fully hereinafter.
Various aspects of the invention are as follows:
A process for the decolorization of alkaline pulp and paper waste waters containing color bodies in weak black liquor, the process comprising the steps of:
A
~L~7~
(a) contacting the waste water with sulfuric acid to adjust the pH to below 2.5;
(b) contacting the resulting solution with anionic polyacrylamide coagulating agent to coagulate the color bodiPs;
(c) separating the solid coagulated color bodies by floatation separation;
(d) contacting the coagulated color bodies with a base to adjust the pH to above ~.O to liquify the color bodies in concentrate form.
A process for the removal of colored bodies in weak black liquor from pulp and paper waste waters containing sulfide and carbonate salts, the process comprising the steps of:
(a) admixing the waste water with mineral acid to adjust the pH to below 2.5 and wi~h polyacrylamide to coagulate the color bodies; and (b) removal of coagulated colored bodies from the surface of waste water, the coagulated colored bodies being carried to the surface of the waste water by means of bubbles of carbon dioxide and reduced sulfur formed in the waste water by reaction of the strong mineral acid with the sulfide and carbonate salts.
A process for the decolorization of alkaline pulp and paper waste waters containing color bodies in weak black liquor, ths process comprising the steps of:
(a) contacting the waste water with a strong mineral acid to adjust the pH to below 2.5;
3Q (b) contacting the resulting solution with polyacrylamide to coagulate the color bodies in the waste water; and Sc) removing the coagulated color bodies from the waste water by floatation separation.
A process for the removal and recovery of color bodies in the form of lignins, and fiber derivatives thereof from alkaline pulp and paper waster waters, the process comprising the steps of:
~Z7~628 - 3a -(a) contacting the waste water with strong mineral acid to adjust the pH to below 2.5;
(b) contacting the resulting acidic waste water with a coagulating agent to coagulate the color bodies in the waste water;
(c) separating the coagulated colored bodies from the waste water;
(d) contacting the separated colored bodies with a strong base to produce a basic pH, thereby causing the colored bodies to become a liquor-pulp mixture in a liquid or colloidal state: and (e) returning the liquor-pulp mixture to the brown stock washing system to recover materials therein;
whereby sludge disposal is reduced and fiber recovered.
By way of added explanation, the concepts of the present invention reside in a process for the decolori~ation of pulp and paper waste water which contain color bodies in which the waste water is first contacted with a strong acid to adjust the pH of the waste water to below 2.5 and then contacting the resulting solution with a coagulating polymer capable of coagulating the olor bodies. The coagulated color bodies can thus be separated efficiently and inexpensively and then returned to a dissolved or suspended state by adjusting the pH of the solid coagulum to about 9. The collected pulp and black liquor mixture can then be conveniently recovered.
It has been surprisingly found, in accordance with the practice of the present invention, that the combination of the steps of acidifying the normally alkaline waste water and contacting the resulting acid solution with coagulants provides a flock which naturally floats. Because the waste water contains a ~ubstantial amount of sulfide and carbonate salts, the acidification step causes carbon dioxide and reduced sulfur gases to be liberated and the coagulated flock is thus carried to the surface of the liquid by means of the escaping gases.
127~i28 That effect exists in providing a substantially complete separation of the color bodies from the waste water in a manner which is more efficient and less expensive than procedures previously used in the prior art.
A waste water from pulp and paper processing which contains color water from pulp and paper processing which contains color bodies, usually in the form of lignins, their oxidation products and their degradation products as well as a substantial amount of pulp and carbonate salts are passed to a reaction vessel where it is intimately admixed with a strong mineral acid, preferably sulphuric acid, to adjust the normal alkaline pH of the waste water to a pH below 2.5 and with a coagulant in a coagulation vessel whereby carbon dioxide and sulfur gases, usually small quantities of hydrogen sulfide, are liberated.
The escaping gases cause the color bodies which have been coagulated to form a flock which rises to the surface of the waste water for separation therefrom in a separation vessel.
The clarified and substantially color reduced ~straw colored) liquid is then removed for additional biological treatment in accordance with conventional processing techniques.
The solid coagulum is then passed to a recovery vessel where it is contacted with a strong base, usually an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide, to adjust the pH of the solid coagulum to a level of about 9. The neutralization of the coagulum thus causes the color to be returned to a liquid or colloidal state to form a ~274~i2~
weak black liquor-pulp mixture which can then be returned to the brown stock washing system typical to all kraft pulp mills. The color bodies present in the black liquor in a suspended or colloidal state have relatively high BTU values, the collected fiber has value in the paper making process. Recovery of 'chese materials in a form compatible with the brown stock washing system represents the reuse of valuable materials and a coincidental reduction of wasted organics from pulp mill waste waters.
As the recovered material is comparable with existing process materials and recovered in existing process equipment, costly sludge disposal is not necessary.
It is also possible to recover sulfur values by simply scrubbing the sulfur gases, notably hydrogen sulfide, with sodium hydroxide in the recovery vessel.
The acid employed in the coagulation step is, as indicated above, preferably a strong mineral acid such as hydrochloric acid, phosphoric acid, nitric acid or sulfuric acid. For reasons of economy and compatibility with paper processing technology, it is generally preferred to employ sulfuric acid as the coagulant. The amount of sulfuric acid can be varied within relatiYely wide limits, depending in large measure on the characteristics of the waste water undergoing treatment. In general, it is preferred to employ an amount of sulfuric acid sufficient to coagulate the color bodies in the waste water and assure that the pH is reduced to below 2.5.
~27~
The coagulant employed in the practiced of this invention can be any of a variety sf coagulants commonly employed in processing of paper waste waters. Par-ticularly preferred are polyacrylamide flocculants, such as the polyacrylamides marketed by Nalco, Chem-Link, Hercules, et al.
The preferred polymers are high molecular weight and anionically charged; typically the higher the molecular weight and charge density, the better the performance. The amount of the flocculant is generally an amount sufficient to substantially completely effect coagulation of the color bodies present. Best results are usually achieved when the ratio of coagulant to acid is within the range of one pound of polymer for each 100 lbs. of sulfuric acid required to reach a pH of 2.5. As will be appreciated by those skilled in the art, greater or lesser quantities of the coagulating agent may be used depending to some extent on the composition of the waste water.
This technique, with some minor modification, primarily the addition of dissovled air in vessel number can be used to separate and remove ligatious material from kraft black liquor. It can also be used to remove ligatious material from pulping waste waters which contain no fiber.
.~ .
It will be understood the various changes and modifications can be made in the details of procedure, formulation and use without departing from the spirit of the invention, especially as defined in the following claims.
S P E C I F I C A T I O N
This invention relates to the decolorization of pulp and paper waste waters, and more particularly to a process for the resource recovery of the organic materials removed by the decolorization process.
Pulp and paper waste waters have presented, for many years, a formidable waste treatment problem. For example, typical kraft pulp mills generate millions of gallons of waste water everyday containing suspended and colloidal solids made up chiefly of pulp fibers and color bodies, usually in the form of lignins and the products of the oxidation and thermal degradation of wood sugars. The latter waste causes the primary concern because of the high biological oxygen demand and non-aesthetic characteristics of such wastes if treated conventionally.
Various techniques have been proposed to remove the colloidal color bodies, suspended solids and associated high BOD. One technique has involved the addition of massive quantities of lime to the waste water from which pulp fibers and ligneous matter have been separated. The lime addition flocculates the color bodies and thereby reduces the initial waste water color of the waste stream by 80-90~ as well as significantly reducing the BOD. That technique has a significant disadvantage in that it involves high capital and operating costs. In addition, such waste water techniques do ~746X8 not allow for reCoYery of the pulp or lignatious material collected by the process. Finally, the quantities of lime employed pose very significant problems in lime handling, sludge removal and ultimate waste water quality.
It has also been proposed to contact sush waste waters with an ion exchange resin which is capable of absorbing the lignins and their derivatives. Ion exchange resins for that purpose have generally been highly cross linked, hydrophilic acrylic copolymers which absorb the organic components by means of Van der Waal's forces.
one of the primary disadvantages of the ion exchange technique is that the resin removes free chloride ions as well as the color bodies. When the ion exchange rQsin is regenerated, the chloride ions thus released have a tendency to build up in the system to create high chloride levels. That method is also extremely costly.
It is accordingly an object of an aspect of the present invention to provide a process of decolorizing pulp and paper waste waters containing color bodies which overcomes the foregoing disadvantages.
It is an object of an aspect of the present invention to provide a process for the decolorization of alkaline pulp and paper waste waters containing as color bodies lignins and derivatives thereof which can be carried out at low cost without substantially capital outlays and which is capable of substantially complete recovery o~ wasted pulp and lignatious materials.
These and other objects of the present invention will appear more fully hereinafter.
Various aspects of the invention are as follows:
A process for the decolorization of alkaline pulp and paper waste waters containing color bodies in weak black liquor, the process comprising the steps of:
A
~L~7~
(a) contacting the waste water with sulfuric acid to adjust the pH to below 2.5;
(b) contacting the resulting solution with anionic polyacrylamide coagulating agent to coagulate the color bodiPs;
(c) separating the solid coagulated color bodies by floatation separation;
(d) contacting the coagulated color bodies with a base to adjust the pH to above ~.O to liquify the color bodies in concentrate form.
A process for the removal of colored bodies in weak black liquor from pulp and paper waste waters containing sulfide and carbonate salts, the process comprising the steps of:
(a) admixing the waste water with mineral acid to adjust the pH to below 2.5 and wi~h polyacrylamide to coagulate the color bodies; and (b) removal of coagulated colored bodies from the surface of waste water, the coagulated colored bodies being carried to the surface of the waste water by means of bubbles of carbon dioxide and reduced sulfur formed in the waste water by reaction of the strong mineral acid with the sulfide and carbonate salts.
A process for the decolorization of alkaline pulp and paper waste waters containing color bodies in weak black liquor, ths process comprising the steps of:
(a) contacting the waste water with a strong mineral acid to adjust the pH to below 2.5;
3Q (b) contacting the resulting solution with polyacrylamide to coagulate the color bodies in the waste water; and Sc) removing the coagulated color bodies from the waste water by floatation separation.
A process for the removal and recovery of color bodies in the form of lignins, and fiber derivatives thereof from alkaline pulp and paper waster waters, the process comprising the steps of:
~Z7~628 - 3a -(a) contacting the waste water with strong mineral acid to adjust the pH to below 2.5;
(b) contacting the resulting acidic waste water with a coagulating agent to coagulate the color bodies in the waste water;
(c) separating the coagulated colored bodies from the waste water;
(d) contacting the separated colored bodies with a strong base to produce a basic pH, thereby causing the colored bodies to become a liquor-pulp mixture in a liquid or colloidal state: and (e) returning the liquor-pulp mixture to the brown stock washing system to recover materials therein;
whereby sludge disposal is reduced and fiber recovered.
By way of added explanation, the concepts of the present invention reside in a process for the decolori~ation of pulp and paper waste water which contain color bodies in which the waste water is first contacted with a strong acid to adjust the pH of the waste water to below 2.5 and then contacting the resulting solution with a coagulating polymer capable of coagulating the olor bodies. The coagulated color bodies can thus be separated efficiently and inexpensively and then returned to a dissolved or suspended state by adjusting the pH of the solid coagulum to about 9. The collected pulp and black liquor mixture can then be conveniently recovered.
It has been surprisingly found, in accordance with the practice of the present invention, that the combination of the steps of acidifying the normally alkaline waste water and contacting the resulting acid solution with coagulants provides a flock which naturally floats. Because the waste water contains a ~ubstantial amount of sulfide and carbonate salts, the acidification step causes carbon dioxide and reduced sulfur gases to be liberated and the coagulated flock is thus carried to the surface of the liquid by means of the escaping gases.
127~i28 That effect exists in providing a substantially complete separation of the color bodies from the waste water in a manner which is more efficient and less expensive than procedures previously used in the prior art.
A waste water from pulp and paper processing which contains color water from pulp and paper processing which contains color bodies, usually in the form of lignins, their oxidation products and their degradation products as well as a substantial amount of pulp and carbonate salts are passed to a reaction vessel where it is intimately admixed with a strong mineral acid, preferably sulphuric acid, to adjust the normal alkaline pH of the waste water to a pH below 2.5 and with a coagulant in a coagulation vessel whereby carbon dioxide and sulfur gases, usually small quantities of hydrogen sulfide, are liberated.
The escaping gases cause the color bodies which have been coagulated to form a flock which rises to the surface of the waste water for separation therefrom in a separation vessel.
The clarified and substantially color reduced ~straw colored) liquid is then removed for additional biological treatment in accordance with conventional processing techniques.
The solid coagulum is then passed to a recovery vessel where it is contacted with a strong base, usually an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide, to adjust the pH of the solid coagulum to a level of about 9. The neutralization of the coagulum thus causes the color to be returned to a liquid or colloidal state to form a ~274~i2~
weak black liquor-pulp mixture which can then be returned to the brown stock washing system typical to all kraft pulp mills. The color bodies present in the black liquor in a suspended or colloidal state have relatively high BTU values, the collected fiber has value in the paper making process. Recovery of 'chese materials in a form compatible with the brown stock washing system represents the reuse of valuable materials and a coincidental reduction of wasted organics from pulp mill waste waters.
As the recovered material is comparable with existing process materials and recovered in existing process equipment, costly sludge disposal is not necessary.
It is also possible to recover sulfur values by simply scrubbing the sulfur gases, notably hydrogen sulfide, with sodium hydroxide in the recovery vessel.
The acid employed in the coagulation step is, as indicated above, preferably a strong mineral acid such as hydrochloric acid, phosphoric acid, nitric acid or sulfuric acid. For reasons of economy and compatibility with paper processing technology, it is generally preferred to employ sulfuric acid as the coagulant. The amount of sulfuric acid can be varied within relatiYely wide limits, depending in large measure on the characteristics of the waste water undergoing treatment. In general, it is preferred to employ an amount of sulfuric acid sufficient to coagulate the color bodies in the waste water and assure that the pH is reduced to below 2.5.
~27~
The coagulant employed in the practiced of this invention can be any of a variety sf coagulants commonly employed in processing of paper waste waters. Par-ticularly preferred are polyacrylamide flocculants, such as the polyacrylamides marketed by Nalco, Chem-Link, Hercules, et al.
The preferred polymers are high molecular weight and anionically charged; typically the higher the molecular weight and charge density, the better the performance. The amount of the flocculant is generally an amount sufficient to substantially completely effect coagulation of the color bodies present. Best results are usually achieved when the ratio of coagulant to acid is within the range of one pound of polymer for each 100 lbs. of sulfuric acid required to reach a pH of 2.5. As will be appreciated by those skilled in the art, greater or lesser quantities of the coagulating agent may be used depending to some extent on the composition of the waste water.
This technique, with some minor modification, primarily the addition of dissovled air in vessel number can be used to separate and remove ligatious material from kraft black liquor. It can also be used to remove ligatious material from pulping waste waters which contain no fiber.
.~ .
It will be understood the various changes and modifications can be made in the details of procedure, formulation and use without departing from the spirit of the invention, especially as defined in the following claims.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the decolorization of alkaline pulp and paper waste waters containing color bodies in weak black liquor, the process comprising the steps of:
(a) contacting the waste water with sulfuric acid to adjust the pH to below 2.5;
(b) contacting the resulting solution with anionic polyacrylamide coagulating agent to coagulate the color bodies;
(c) separating the solid coagulated color bodies by floatation separation;
(d) contacting the coagulated color bodies with a base to adjust the pH to above 9.0 to liquify the color bodies in concentrate form.
(a) contacting the waste water with sulfuric acid to adjust the pH to below 2.5;
(b) contacting the resulting solution with anionic polyacrylamide coagulating agent to coagulate the color bodies;
(c) separating the solid coagulated color bodies by floatation separation;
(d) contacting the coagulated color bodies with a base to adjust the pH to above 9.0 to liquify the color bodies in concentrate form.
2. A process for the removal of colored bodies in weak black liquor from pulp and paper waste waters containing sulfide and carbonate salts, the process comprising the steps of:
(a) admixing the waste water with mineral acid to adjust the pH to below 2.5 and with polyacrylamide to coagulate the color bodies: and (b) removal of coagulated colored bodies from the surface of waste water, the coagulated colored bodies being carried to the surface of the waste water by means of bubbles of carbon dioxide and reduced sulfur formed in the waste water by reaction of the strong mineral acid with the sulfide and carbonate salts.
(a) admixing the waste water with mineral acid to adjust the pH to below 2.5 and with polyacrylamide to coagulate the color bodies: and (b) removal of coagulated colored bodies from the surface of waste water, the coagulated colored bodies being carried to the surface of the waste water by means of bubbles of carbon dioxide and reduced sulfur formed in the waste water by reaction of the strong mineral acid with the sulfide and carbonate salts.
3. The process of Claim 2 wherein the mineral acid is sulfuric acid.
4. A process for the decolorization of alkaline pulp and paper waste waters containing color bodies in weak black liquor, the process comprising the steps of:
(a) contacting the waste water with a strong mineral acid to adjust the pH to below 2.5;
(b) contacting the resulting solution with polyacrylamide to coagulate the color bodies in the waste water; and (c) removing the coagulated color bodies from the waste water by floatation separation.
(a) contacting the waste water with a strong mineral acid to adjust the pH to below 2.5;
(b) contacting the resulting solution with polyacrylamide to coagulate the color bodies in the waste water; and (c) removing the coagulated color bodies from the waste water by floatation separation.
5. The process of Claim 4, further comprising the step of contacting the removed coagulated color bodies with a strong base to result in a pH of about 9, causing the colored bodies to become a liquor-pulp mixture in a fluid state.
6. A process as claimed in Claim 4 wherein the mineral acid is sulfuric acid.
7. A process as claimed in Claim 4 which includes the step of scrubbing the sulfur gases being produced by reaction of the mineral acid with the waste water to recover sulfur values therefrom.
8. A process for the removal and recovery of color bodies in the form of lignins, and fiber derivatives thereof from alkaline pulp and paper waster waters, the process comprising the steps of:
(a) contacting the waste water with strong mineral acid to adjust the pH to below 2.5;
(b) contacting the resulting acidic waste water with a coagulating agent to coagulate the color bodies in the waste water;
(c) separating the coagulated colored bodies from the waste water;
(d) contacting the separated colored bodies with a strong base to produce a basic pH, thereby causing the colored bodies to become a liquor-pulp mixture in a liquid or colloidal state; and (e) returning the liquor-pulp mixture to the brown stock washing system to recover materials therein;
whereby sludge disposal is reduced and fiber recovered.
(a) contacting the waste water with strong mineral acid to adjust the pH to below 2.5;
(b) contacting the resulting acidic waste water with a coagulating agent to coagulate the color bodies in the waste water;
(c) separating the coagulated colored bodies from the waste water;
(d) contacting the separated colored bodies with a strong base to produce a basic pH, thereby causing the colored bodies to become a liquor-pulp mixture in a liquid or colloidal state; and (e) returning the liquor-pulp mixture to the brown stock washing system to recover materials therein;
whereby sludge disposal is reduced and fiber recovered.
9. A process as claimed in Claim 8 wherein the base sodium hydroxide.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000512305A CA1274628A (en) | 1986-06-24 | 1986-06-24 | Pulp decolor process |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000512305A CA1274628A (en) | 1986-06-24 | 1986-06-24 | Pulp decolor process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1274628A true CA1274628A (en) | 1990-09-25 |
Family
ID=4133417
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000512305A Expired - Fee Related CA1274628A (en) | 1986-06-24 | 1986-06-24 | Pulp decolor process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1274628A (en) |
-
1986
- 1986-06-24 CA CA000512305A patent/CA1274628A/en not_active Expired - Fee Related
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |