CA1283256C - Method of recovering caustic soda from spent pulping liquors - Google Patents
Method of recovering caustic soda from spent pulping liquorsInfo
- Publication number
- CA1283256C CA1283256C CA000554752A CA554752A CA1283256C CA 1283256 C CA1283256 C CA 1283256C CA 000554752 A CA000554752 A CA 000554752A CA 554752 A CA554752 A CA 554752A CA 1283256 C CA1283256 C CA 1283256C
- Authority
- CA
- Canada
- Prior art keywords
- liquor
- sodium
- spent
- metallic
- metallic oxide
- 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 - Lifetime
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/12—Combustion of pulp liquors
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/0085—Introduction of auxiliary substances into the regenerating system in order to improve the performance of certain steps of the latter, the presence of these substances being confined to the regeneration cycle
- D21C11/0092—Substances modifying the evaporation, combustion, or thermal decomposition processes of black liquor
Landscapes
- Paper (AREA)
Abstract
METHOD OF RECOVERING CAUSTIC
SODA FROM SPENT PULPING LIQUORS
ABSTRACT
A method of recovering sodium hydroxide from alkaline or neutral spent pulping liquor by the addition of metallic oxides, with the exclusion of a Sc, Ti, V, Fe, Cu, Cd or Hg oxide, to the spent liquor in order to directly convert sodium carbonate into sodium hydroxide, followed by separation and recycling of the metallic oxides to the spent liquor.
SODA FROM SPENT PULPING LIQUORS
ABSTRACT
A method of recovering sodium hydroxide from alkaline or neutral spent pulping liquor by the addition of metallic oxides, with the exclusion of a Sc, Ti, V, Fe, Cu, Cd or Hg oxide, to the spent liquor in order to directly convert sodium carbonate into sodium hydroxide, followed by separation and recycling of the metallic oxides to the spent liquor.
Description
FIELD OF THE INVENTION
The present invention relates to a method for directly obtaining sodium hydroxide (caustic soda) from alkaline or neutral spent pulping liquor.
DESCRIPTION OF PRIOR~
0 In many prior art, alkaline pulping processes (one prior art process is schematically shown in figure 1), wood chips are digested in an aqueous pulping liquor containing sodium hydroxide. If the liquor also contains sodium sulfide, the process is kraft. After digestion is complete, the spent liquor (black liquor) is recycled to regenerate the sodium hydroxide.
The organic matter in the concentrated black liquor is then burned and the resulting smelt is dissolved in water to produce green liquor, which contains sodium carbonate.
The carbonate present in this liquor is not sufficiently alkaline to pulp wood or similar fibrous materials to an adequate degree. Therefore the carbonate is subsequently reacted with an hydroxide, and transformed into sodium hydroxide, by the process called "causticising". The carbonate thus obtained has a low solubility in the liquor, and is eliminated from the system by sedimentation and/or filtration. In practice, calcium carbonate is separated after reacting with calcium hydroxide, heated until it is transformed into calcium oxide and, by dissolution in water, restored to hydroxide form.
The causticising step not only requires time and equipment, but the resulting liquor still contains a significant concentration of sodium carbonate.
i ~L~83~6 The present invention is intended to considerably reduce or entirely eliminate th~ "causticising" step, the so called "green liquor", the calcium hydroxide normally re~uired for the regeneration of sodium hydroxide, the time and heat to convert the calcium carbonate into oxide, the equipment used, and ultimately increase production while reducing costs.
OBJECTS OF THE PRESENT INVENTION
One object of the present invention is to provide a method to recover the cooking chemicals from the spent pulping liquors.
Another object of the present invention is to provide a method to recover the cooking chemicals from the spent pulping liquors using certain metallic oxides which are subsequently separated from the spent liguor and recycled.
- Still another object of the present invention is to provide a method of obtaining caustic soda which will help reducing the required capacity of the clarifiers, settling tanks, storage tanks and the like, that are generally used in these industries.
Another object of the present invention is to provide a method for directly and economically obtaining caustic soda by way of combusting the spent cooking liquor in the pulp and paper industry.
These and other objects of the present invention will be obtained generally by a method of recovering sodium hydroxide from spent pulping liquor, wherein the lignin rich spent liquor is roasted at a temperature in excess of 700C with oxygen to obtain sodium carbonate, carbon - :
~L2~ 5~
dloxide and water, the imp~ovement comprising:
- selecting a metallic oxide from the transition elements other than a Sc, Ti, V, Fe, Cu, Cd or Hg oxide;
- reacting said metallic oxide with the sodium carbonate present in said spent liquor so as to obtain an oxidized sodium metallic salt and carbon I0 dioxide, the reaction being made in stoichiometric ratio;
- hydrolysis of said oxidized sodium metallic salt to obtain the desired sodium hydroxide and recover said I5 metallic oxide;
- recuperation of said metallic oxide.
The purpose of using metallic oxide other than a Sc, Ti, Vl Fe, Cu, Cd or Hg oxide is to avoid unwanted metallic sulfides such as Ferrus sulphide. The metallic oxide is preferably manganese dioxide in view of its availability at a reasonable cost. Ce or Cr oxides can also be used.
DESCRIPTION OF DRAWINGS
The invention will now be described in detail with reference to a specific embodiment thereof which is illustrated by way of example in the accompanying drawings, in which:
Figure 1 is a block flow chart diagram showing a typical prior art process.
Figure 2 is a block flow chart diagram of a process embodying the present invention.
~ ,~
~33~56 DESCRIPTION OF A PREYERRED EMBODIMENT
The causticising procedure embodied in this invention will be refexred to as the "autocausticising system".
The principle of this invention consists of using an appropriate metallic oxide to produce an intermediate oxidized sodium metallic salt which is then hydrolyzed to produce the sodium hydroxide and the original metallic 0 oxide which may be used again and again.
1 ) COMBUSTION PHASE
A) Normal reaction Lignin + xO2 -----> Na2CO3 ~ YC02 + zH20 B) Intermediate reaction Na2CO3 + MexOy -~ > Na20.MexOy ~ CO2 The sodium carbonate reacts with the metallic oxides to produce an oxidized sodium metallic salt and carbon dioxide. This reaction take~ place during the combustion phase at a temperature in excess of 700C.
It is important to mention that the meta'lic oxides concentration in the liquor must, at all time, be in stoichiometric ratio with the sodium carbonate~
The present invention relates to a method for directly obtaining sodium hydroxide (caustic soda) from alkaline or neutral spent pulping liquor.
DESCRIPTION OF PRIOR~
0 In many prior art, alkaline pulping processes (one prior art process is schematically shown in figure 1), wood chips are digested in an aqueous pulping liquor containing sodium hydroxide. If the liquor also contains sodium sulfide, the process is kraft. After digestion is complete, the spent liquor (black liquor) is recycled to regenerate the sodium hydroxide.
The organic matter in the concentrated black liquor is then burned and the resulting smelt is dissolved in water to produce green liquor, which contains sodium carbonate.
The carbonate present in this liquor is not sufficiently alkaline to pulp wood or similar fibrous materials to an adequate degree. Therefore the carbonate is subsequently reacted with an hydroxide, and transformed into sodium hydroxide, by the process called "causticising". The carbonate thus obtained has a low solubility in the liquor, and is eliminated from the system by sedimentation and/or filtration. In practice, calcium carbonate is separated after reacting with calcium hydroxide, heated until it is transformed into calcium oxide and, by dissolution in water, restored to hydroxide form.
The causticising step not only requires time and equipment, but the resulting liquor still contains a significant concentration of sodium carbonate.
i ~L~83~6 The present invention is intended to considerably reduce or entirely eliminate th~ "causticising" step, the so called "green liquor", the calcium hydroxide normally re~uired for the regeneration of sodium hydroxide, the time and heat to convert the calcium carbonate into oxide, the equipment used, and ultimately increase production while reducing costs.
OBJECTS OF THE PRESENT INVENTION
One object of the present invention is to provide a method to recover the cooking chemicals from the spent pulping liquors.
Another object of the present invention is to provide a method to recover the cooking chemicals from the spent pulping liquors using certain metallic oxides which are subsequently separated from the spent liguor and recycled.
- Still another object of the present invention is to provide a method of obtaining caustic soda which will help reducing the required capacity of the clarifiers, settling tanks, storage tanks and the like, that are generally used in these industries.
Another object of the present invention is to provide a method for directly and economically obtaining caustic soda by way of combusting the spent cooking liquor in the pulp and paper industry.
These and other objects of the present invention will be obtained generally by a method of recovering sodium hydroxide from spent pulping liquor, wherein the lignin rich spent liquor is roasted at a temperature in excess of 700C with oxygen to obtain sodium carbonate, carbon - :
~L2~ 5~
dloxide and water, the imp~ovement comprising:
- selecting a metallic oxide from the transition elements other than a Sc, Ti, V, Fe, Cu, Cd or Hg oxide;
- reacting said metallic oxide with the sodium carbonate present in said spent liquor so as to obtain an oxidized sodium metallic salt and carbon I0 dioxide, the reaction being made in stoichiometric ratio;
- hydrolysis of said oxidized sodium metallic salt to obtain the desired sodium hydroxide and recover said I5 metallic oxide;
- recuperation of said metallic oxide.
The purpose of using metallic oxide other than a Sc, Ti, Vl Fe, Cu, Cd or Hg oxide is to avoid unwanted metallic sulfides such as Ferrus sulphide. The metallic oxide is preferably manganese dioxide in view of its availability at a reasonable cost. Ce or Cr oxides can also be used.
DESCRIPTION OF DRAWINGS
The invention will now be described in detail with reference to a specific embodiment thereof which is illustrated by way of example in the accompanying drawings, in which:
Figure 1 is a block flow chart diagram showing a typical prior art process.
Figure 2 is a block flow chart diagram of a process embodying the present invention.
~ ,~
~33~56 DESCRIPTION OF A PREYERRED EMBODIMENT
The causticising procedure embodied in this invention will be refexred to as the "autocausticising system".
The principle of this invention consists of using an appropriate metallic oxide to produce an intermediate oxidized sodium metallic salt which is then hydrolyzed to produce the sodium hydroxide and the original metallic 0 oxide which may be used again and again.
1 ) COMBUSTION PHASE
A) Normal reaction Lignin + xO2 -----> Na2CO3 ~ YC02 + zH20 B) Intermediate reaction Na2CO3 + MexOy -~ > Na20.MexOy ~ CO2 The sodium carbonate reacts with the metallic oxides to produce an oxidized sodium metallic salt and carbon dioxide. This reaction take~ place during the combustion phase at a temperature in excess of 700C.
It is important to mention that the meta'lic oxides concentration in the liquor must, at all time, be in stoichiometric ratio with the sodium carbonate~
2) HY~ROLYSIS PHASE
Na20.MexOy + H20 -----> 2NaOH + MexOy The oxidized sodium metallic salt is then hydrolyzed to obtain the desired sodium hydroxide and metallic oxide. The latter is recuperated and separated from impurities for future uses.
33~5t~
This "autocausticisinq system" can also be referred to as a "dry" causticising process or a direct process, as reaction lB) takes place during the combustion phase.
To make the autocausticising system economical, it is necessary to separate the metallic oxides produced during the hydrolysis phase from other undesirable solids and recycle them. The metallic oxides are first separated according to specific gravity, by the gravity method or by known centrifugal means.
The level of solid material retained in the separators can be controlled by an outlet metering device such as a rotary feeder. The separated metallic oxides can be allowed to settle in a decanting tank to prevent weak liquor from being recycled instead of the metallic oxide. The decanting tank level can also be controlled by an outlet metering device, to regulate the recycling of said oxides into the liquor.
The point of entry of the recycled metallic oxides is selected for good mixing with the spent liquor stream. The liquid overflowing from the decanting tank is returned to the dissolving tank.
One preferred metallic oxide is manganese dioxide ~MnO2).
Having thus described the invention in such full, clear, concise and exact terms as to enable any person sXilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, the applicant states that the subject which he regards as being his invention is particularly pointed out and distinctly claimed in what is claimed. It is to be understood that equivalents or modifications of, or substitutions for, parts of the above specifically 33~;6 described embodiments of the invention may be made without departing from the scope of the invention as set forth in what is claimed.
For example, in the previous explained embodiment, the reaction has been described with sodium hydroxide, however, it is within the scope and spirit of the present invention to use potassium hydroxide for the same purpose.
Na20.MexOy + H20 -----> 2NaOH + MexOy The oxidized sodium metallic salt is then hydrolyzed to obtain the desired sodium hydroxide and metallic oxide. The latter is recuperated and separated from impurities for future uses.
33~5t~
This "autocausticisinq system" can also be referred to as a "dry" causticising process or a direct process, as reaction lB) takes place during the combustion phase.
To make the autocausticising system economical, it is necessary to separate the metallic oxides produced during the hydrolysis phase from other undesirable solids and recycle them. The metallic oxides are first separated according to specific gravity, by the gravity method or by known centrifugal means.
The level of solid material retained in the separators can be controlled by an outlet metering device such as a rotary feeder. The separated metallic oxides can be allowed to settle in a decanting tank to prevent weak liquor from being recycled instead of the metallic oxide. The decanting tank level can also be controlled by an outlet metering device, to regulate the recycling of said oxides into the liquor.
The point of entry of the recycled metallic oxides is selected for good mixing with the spent liquor stream. The liquid overflowing from the decanting tank is returned to the dissolving tank.
One preferred metallic oxide is manganese dioxide ~MnO2).
Having thus described the invention in such full, clear, concise and exact terms as to enable any person sXilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, the applicant states that the subject which he regards as being his invention is particularly pointed out and distinctly claimed in what is claimed. It is to be understood that equivalents or modifications of, or substitutions for, parts of the above specifically 33~;6 described embodiments of the invention may be made without departing from the scope of the invention as set forth in what is claimed.
For example, in the previous explained embodiment, the reaction has been described with sodium hydroxide, however, it is within the scope and spirit of the present invention to use potassium hydroxide for the same purpose.
Claims (7)
1. A method of recovering sodium hydroxide from spent pulping liquor, wherein the lignin rich spent liquor is roasted at a temperature in excess of 700°C with oxygen to obtain sodium carbonate, carbon dioxide and water, the improvement comprising:
- selecting a metallic oxide from the transition elements other than a Sc, Ti, V, Fe, Cu, Cd or Hg oxide;
- reacting said metallic oxide with the sodium carbonate present in said spent liquor so as to obtain an oxidized sodium metallic salt and carbon dioxide, the reaction being made in stoichiometric ratio;
- hydrolysis of said oxidized sodium metallic salt to obtain the desired sodium hydroxide and recover said metallic oxide;
- recuperation of said metallic oxide.
- selecting a metallic oxide from the transition elements other than a Sc, Ti, V, Fe, Cu, Cd or Hg oxide;
- reacting said metallic oxide with the sodium carbonate present in said spent liquor so as to obtain an oxidized sodium metallic salt and carbon dioxide, the reaction being made in stoichiometric ratio;
- hydrolysis of said oxidized sodium metallic salt to obtain the desired sodium hydroxide and recover said metallic oxide;
- recuperation of said metallic oxide.
2) A method according to claim 1 wherein the metallic oxide reacted with said sodium carbonate is obtained from said recuperation from a previous reaction.
3) A method according to claim 1 or 2, wherein the metallic oxide is selected from Mn, Ce or Cr.
4) A method according to claim 1 or 2 wherein the metallic oxide is manganese dioxide.
5) A method according to claim 1 or 2, wherein the recuperation is achieved by separation using gravity or a centrifugal separator.
6) A method of recovering sodium hydroxide from spent pulping liquor, wherein the lignin rich spent liquor is roasted at a temperature in excess of 700°C with oxygen to obtain sodium carbonate, carbon dioxide and water, the improvement comprising:
- reacting manganese dioxide with the sodium carbonate present in spent liquor so as to obtain an oxidized sodium manganese salt and carbon dioxide, the reaction being made in stoichiometric ratio;
- hydrolysis of said oxidized sodium manganese salt to obtain the desired sodium hydroxide and recover said manganese dioxide;
- recuperation of said manganese dioxide.
- reacting manganese dioxide with the sodium carbonate present in spent liquor so as to obtain an oxidized sodium manganese salt and carbon dioxide, the reaction being made in stoichiometric ratio;
- hydrolysis of said oxidized sodium manganese salt to obtain the desired sodium hydroxide and recover said manganese dioxide;
- recuperation of said manganese dioxide.
7) A method according to claim 6 wherein the recuperation is achieved by separation using gravity or a centrifugal separator.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000554752A CA1283256C (en) | 1987-12-18 | 1987-12-18 | Method of recovering caustic soda from spent pulping liquors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000554752A CA1283256C (en) | 1987-12-18 | 1987-12-18 | Method of recovering caustic soda from spent pulping liquors |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1283256C true CA1283256C (en) | 1991-04-23 |
Family
ID=4137102
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000554752A Expired - Lifetime CA1283256C (en) | 1987-12-18 | 1987-12-18 | Method of recovering caustic soda from spent pulping liquors |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1283256C (en) |
-
1987
- 1987-12-18 CA CA000554752A patent/CA1283256C/en not_active Expired - Lifetime
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |