CA1066697A - Method of producing cellulose - Google Patents
Method of producing celluloseInfo
- Publication number
- CA1066697A CA1066697A CA259,578A CA259578A CA1066697A CA 1066697 A CA1066697 A CA 1066697A CA 259578 A CA259578 A CA 259578A CA 1066697 A CA1066697 A CA 1066697A
- Authority
- CA
- Canada
- Prior art keywords
- raw material
- liquor
- temperature
- cooking
- chemical activity
- 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
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
- D21C3/00—Pulping cellulose-containing materials
- D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
-
- 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
- D21C3/00—Pulping cellulose-containing materials
- D21C3/22—Other features of pulping processes
- D21C3/26—Multistage processes
Landscapes
- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides a method of manufacturing a chemical pulp from a fibrous raw material which comprises homogeneously impregnating the fibrous raw material with an alkali solution of weaker chemical activity whereby to minimize delignification of said raw material, subjecting said alkali impregnated raw material to mechanical defibration and treating said defibrated raw material with an alkali solution of stronger chemical activity to effect delignification thereof.
The present invention provides a method of manufacturing a chemical pulp from a fibrous raw material which comprises homogeneously impregnating the fibrous raw material with an alkali solution of weaker chemical activity whereby to minimize delignification of said raw material, subjecting said alkali impregnated raw material to mechanical defibration and treating said defibrated raw material with an alkali solution of stronger chemical activity to effect delignification thereof.
Description
^ 10666g7 ~ I The present invention relates to the production of a doli~uificd chemical cellulose pulp.
Cellulose or pulp for the manufacture of paper or for chemical purposes is manufactured from fibrous raw materials primarily wood. In such processes of manufacture the binding substance between the fibres i.e. the lignin for the paper pulp is dissolved with as little as possible extraction or degradation of the holo-cellulose components of the raw material.
Conventional processes for the production of such pulps have heretofore primarily been the sulphite process and the sulphate process. In the sulphite process fibrous raw material is delignified by cooking with a bisulphite solution containing calcium, magnesium, sodium or ammonium. In the -sulphate process, the fibrous raw material is cooked with a solution of caustic soda and sodium sulphide. The sodium c~m~ D r~ents valu~ are subsequently recovered, and to make up for losses, - sulphate is added in a recovery process. The deliquification can also be carried out in the soda process without sulphide, using caustic soda for make-up, giving however, under conven-tional conditions, a lower yield of pulp with inferior physical properties.
The most common fibrous raw material used is wood which is normally chipped to pieces of 15-25 mm in length, 10-20 mm in width and 3-8 mm in thickness. The chips are impreg- -nated with the cooking liquor to various degrees of penetration -and then cooked at elevated temperature and pressure until a desired amount of lignin has been dissolved. In the alkaline processes i.e. the sulphate and soda processes the impregnation -of the cooking liquor takes place in both the fiber direction and perpendicular to this direction at essentially ~fi~ the same speed. When the cooking liquor passes through the chip the wood absorbs alkali and the impregnated liquor becomes - 1- ~
~0666g7 gradually weaker. Depending on the thickness of the chips, there is an accentuated difference in alkali concentration in the liquor between the outer and inner parts of the chips up to the extreme condition of zero alkali in the center of the chips. The consequence of this is that the outer parts of the chi~s will~ e overcooked and the lnner parts undercooked ~ hu ' or even h~draoli~od, yielding less pulp than expected at a certain degree of delignification and with reduced strength - ~ -properties.
In the process disclosed in U.S. Patent No. 2,904,460 -William J. Nolan partly removed this disadvantage partly by shredding the chips to splinters before cooking, the splinters having a cross-sectional dimension of about 2.3 to about 4.7 ~
mm. By doing so, he also reduced substantially the cooking time -from the conventional 1-3 hours to 15-25 minutes. In order to - -further improve the process the applicants Companhia Suzano de ; Papel e Celulose, in Brazilian No. 205,374 proposed a method to delignify a defibered fiberous raw material in which in order to achieve defibration of the raw material without damaging the fiber walls, the raw material e.g. wood chips is reduced to match stick size, which sticks are completely and homogeneous-ly impregnated with cooking li~uor at a temperature of 120-130C.
The temperature is then raised to a cooking temperature of 160-180C, at which temperature the lignin is perfectly thermoplastic.
In a subsequent mechanical defibration, the separation of the fibers occur in the binding lignin. Cooking of the defibered raw material is then carried out rapidly in 2-5 minutes. The advantages of the process include (a) a very fast process compared to conventional processes. (b) An absolutely homo-geneous end product. (c) An increased yield, essentially dueto the short reaction time.
In U.S. Patent No. 3,773,610 to Joseph C. Chouvlin et. al.
' ,.: . :
Cellulose or pulp for the manufacture of paper or for chemical purposes is manufactured from fibrous raw materials primarily wood. In such processes of manufacture the binding substance between the fibres i.e. the lignin for the paper pulp is dissolved with as little as possible extraction or degradation of the holo-cellulose components of the raw material.
Conventional processes for the production of such pulps have heretofore primarily been the sulphite process and the sulphate process. In the sulphite process fibrous raw material is delignified by cooking with a bisulphite solution containing calcium, magnesium, sodium or ammonium. In the -sulphate process, the fibrous raw material is cooked with a solution of caustic soda and sodium sulphide. The sodium c~m~ D r~ents valu~ are subsequently recovered, and to make up for losses, - sulphate is added in a recovery process. The deliquification can also be carried out in the soda process without sulphide, using caustic soda for make-up, giving however, under conven-tional conditions, a lower yield of pulp with inferior physical properties.
The most common fibrous raw material used is wood which is normally chipped to pieces of 15-25 mm in length, 10-20 mm in width and 3-8 mm in thickness. The chips are impreg- -nated with the cooking liquor to various degrees of penetration -and then cooked at elevated temperature and pressure until a desired amount of lignin has been dissolved. In the alkaline processes i.e. the sulphate and soda processes the impregnation -of the cooking liquor takes place in both the fiber direction and perpendicular to this direction at essentially ~fi~ the same speed. When the cooking liquor passes through the chip the wood absorbs alkali and the impregnated liquor becomes - 1- ~
~0666g7 gradually weaker. Depending on the thickness of the chips, there is an accentuated difference in alkali concentration in the liquor between the outer and inner parts of the chips up to the extreme condition of zero alkali in the center of the chips. The consequence of this is that the outer parts of the chi~s will~ e overcooked and the lnner parts undercooked ~ hu ' or even h~draoli~od, yielding less pulp than expected at a certain degree of delignification and with reduced strength - ~ -properties.
In the process disclosed in U.S. Patent No. 2,904,460 -William J. Nolan partly removed this disadvantage partly by shredding the chips to splinters before cooking, the splinters having a cross-sectional dimension of about 2.3 to about 4.7 ~
mm. By doing so, he also reduced substantially the cooking time -from the conventional 1-3 hours to 15-25 minutes. In order to - -further improve the process the applicants Companhia Suzano de ; Papel e Celulose, in Brazilian No. 205,374 proposed a method to delignify a defibered fiberous raw material in which in order to achieve defibration of the raw material without damaging the fiber walls, the raw material e.g. wood chips is reduced to match stick size, which sticks are completely and homogeneous-ly impregnated with cooking li~uor at a temperature of 120-130C.
The temperature is then raised to a cooking temperature of 160-180C, at which temperature the lignin is perfectly thermoplastic.
In a subsequent mechanical defibration, the separation of the fibers occur in the binding lignin. Cooking of the defibered raw material is then carried out rapidly in 2-5 minutes. The advantages of the process include (a) a very fast process compared to conventional processes. (b) An absolutely homo-geneous end product. (c) An increased yield, essentially dueto the short reaction time.
In U.S. Patent No. 3,773,610 to Joseph C. Chouvlin et. al.
' ,.: . :
- 2 -. .
. . . .
-: . :,, j . ". . ..
; ~066697 a very similar process is disclosed in which the inventors however failed to recognize the importance of the use of small sticks of thin chips rather than conventional mill sized chips.
This is fundamental not only to obtain a homogeneous impregna-tion and thus a homogeneous end product but also to achieve a homogeneous heating of the impregnated chips before defibrating.
If the chips are not hot enough in the inner parts, the fiber walls of these parts will be damaged during the mechanical - defibration. If, however, heating is carried out slowly enough ~ 10 to permit perfect penetration of the heat to the center of the - chips, substantlal delignification will take place before de-fibering and the fiber walls will be damaged because the fibers will not have the necessary protection of an intact lignin layer during the defibering process.
- Laboratory tests carried out on Eucalyptus wood using a cooking liquor with 25~ sulphidity have qiven the following comparative results:
T~ LE -20 ~ Time to Time at Screened Strength -170C170 C yield at at l~C.S.
min min 15 PN Fre~
. .. _ . ....... ... ...
Tensil Tear Conventional cooking 60 30 51.0 9190 80 Nolan 0 20 54.8 12000 91 Chouvlin 10 3 49.0 8500 82 ¦3 15S.0 ~ llE00 All these methods, however, have a common disadvantage namely the cooking liquor used for impregnation penetrates into the lumen i.e. the hollow parts of the fibers where the cellulose components of the wood are not protected by a lignin layer and at temperatures between 120C and 170C the dissolution of .^, ~066697 cellulose components, especially the pentosanes, is already substantial, and at 170C or more, serious. This explains why the yield of a raw material, containing 30~ or less lignin, is only about 50~.
It has now been found that the disadvantage may be substantially avoided when the impregnation of the fibrous raw material is effected with any alkali agent of reduced or ~
weakened chemical activity and preferably sodium carbonate with ~ -or without sodium sulphide, available in sulphate mills in the form of "green liquor~, mixed with used cooking liquor, black liquor, containing normally about S to 10 g/l active alkali, most of which in form of sodium sulphide.
This liquor dissolves little or no cellulose sub-stance during the impregnation and heating periods but prevents r ~ the formation of acid conditions and thus hydrolysis during ~ C
impregnation and defibration periods of the process.
- Agents with high chemical activity such as caustic soda with or without sodium sulphide, e.g. white liquor in the sulphate mills, is added during the defibration or immediately thereafter. This liquor, when added, will dissolve the lignin layer on the outside of the fibers, exposed by the defibering process, but the hollow inside parts of the fibers remain pro-tected by the impregnation liquor during the short period of 2-5 minutes the cooking will take.
According to the present invention therefore there is provided a method of manufacturing a chemical pulp from a fibrous raw material which comprises homogeneously impregnating the fib-rous raw material with an alkali solution of weaker chemical activity whereby to minimize delignification of said raw material, subjecting said alkali impregnated raw material to mechanical defibration and treating said defibrated raw material with an alkali solution of stronger chemical activity to effect deligni-~066697 fication thereof.
The method of the present invention has given sur-prisingly good results. Thus, impregnating shredded chips of Eucalyptus of about 2 by 2 mm section at 125C during 5 minutes with a mixture of green liquor and black liquor with a total alkali content of 8~ based on dry wood weight, raising the temperature in 15 secor.ds by direct injection of steam to 170C, defibrating the material at this temperature, adding in the defibration white liquor with 25% sulphidity containing 10%
active alkali based on dry wood and cooking the defibered mat-erial during 3 minutes, the following results have been obtained: -Screened yield: 60.1%
Tensil strength: 12,500 -Tear strength: 118 Tests also indicate that essentially the same results may be achieved without adding sodium sulphide to the process, -thus allowing for a sulphur-free high yield, high quality pulping process. This process adapts itself perfectly to the deligni-fication of fiberous raw material with oxygen in an alkali solution. Laboratory tests have been carried out with Eucalyptus wood and it i8 anticipated corresponding improvements will be achieved using any wood or other fiberous raw material as for example sugar cane bagasse and bamboo.
Due to the fact that the delignification i8 effected on defibered raw material, the process is independent of the - ~ density of this raw material. Thus, a heterogeneous raw material such as mixed hardwoods or a mixture of softwood and hardwood or a mixture of bamboo and wood of any kind will give a homogen-eous end product. The pieces of the raw material must not nec-essarily be in the form of normal chips, reduced to sticks of about 2 to 3 mm section. The chips of constant thickness as produced in a drum chipper are very well suited for the process.
_ 5 _ -.`; : `
- , . . . . : .: . .. .
1066~
The ideal thickness of the chips is about 2 mm. Length and width can vary within any practical limit. Normal sized chips as used in pulp mills may be used but with the disadvantage of not achieving a homogeneous impregnation and heating through the chips, resulting in increased reaction time and decreased yield and strength properties of the pulp.
Impregnation of the raw material with green liquor or any other slow acting alkali agent followed by cooking with a B fast acting alkali agent is/little advantage if not used in combination with defibering the raw material between impregnation and cooking, because only in this way the selective dissolving of lignin by the white liquor can take place as described above.
In addition to the advantages already described the process of the present invention results in less organic sub-stance per ton of pulp to be treated in the recovery system and thus higher capacity in terms of ton of pulp/day in existing plants or smaller and thus cheaper units in new plants. Only part - about 50% - of the green liquor will be transformed into white liquor in the causticizing plant, giving correspondingly higher capacity in existing installations or smaller new in-stallations. This also applies to the reburning plant for lime sludge .
'; ' ,~
~
. : '' :
. . . .
-: . :,, j . ". . ..
; ~066697 a very similar process is disclosed in which the inventors however failed to recognize the importance of the use of small sticks of thin chips rather than conventional mill sized chips.
This is fundamental not only to obtain a homogeneous impregna-tion and thus a homogeneous end product but also to achieve a homogeneous heating of the impregnated chips before defibrating.
If the chips are not hot enough in the inner parts, the fiber walls of these parts will be damaged during the mechanical - defibration. If, however, heating is carried out slowly enough ~ 10 to permit perfect penetration of the heat to the center of the - chips, substantlal delignification will take place before de-fibering and the fiber walls will be damaged because the fibers will not have the necessary protection of an intact lignin layer during the defibering process.
- Laboratory tests carried out on Eucalyptus wood using a cooking liquor with 25~ sulphidity have qiven the following comparative results:
T~ LE -20 ~ Time to Time at Screened Strength -170C170 C yield at at l~C.S.
min min 15 PN Fre~
. .. _ . ....... ... ...
Tensil Tear Conventional cooking 60 30 51.0 9190 80 Nolan 0 20 54.8 12000 91 Chouvlin 10 3 49.0 8500 82 ¦3 15S.0 ~ llE00 All these methods, however, have a common disadvantage namely the cooking liquor used for impregnation penetrates into the lumen i.e. the hollow parts of the fibers where the cellulose components of the wood are not protected by a lignin layer and at temperatures between 120C and 170C the dissolution of .^, ~066697 cellulose components, especially the pentosanes, is already substantial, and at 170C or more, serious. This explains why the yield of a raw material, containing 30~ or less lignin, is only about 50~.
It has now been found that the disadvantage may be substantially avoided when the impregnation of the fibrous raw material is effected with any alkali agent of reduced or ~
weakened chemical activity and preferably sodium carbonate with ~ -or without sodium sulphide, available in sulphate mills in the form of "green liquor~, mixed with used cooking liquor, black liquor, containing normally about S to 10 g/l active alkali, most of which in form of sodium sulphide.
This liquor dissolves little or no cellulose sub-stance during the impregnation and heating periods but prevents r ~ the formation of acid conditions and thus hydrolysis during ~ C
impregnation and defibration periods of the process.
- Agents with high chemical activity such as caustic soda with or without sodium sulphide, e.g. white liquor in the sulphate mills, is added during the defibration or immediately thereafter. This liquor, when added, will dissolve the lignin layer on the outside of the fibers, exposed by the defibering process, but the hollow inside parts of the fibers remain pro-tected by the impregnation liquor during the short period of 2-5 minutes the cooking will take.
According to the present invention therefore there is provided a method of manufacturing a chemical pulp from a fibrous raw material which comprises homogeneously impregnating the fib-rous raw material with an alkali solution of weaker chemical activity whereby to minimize delignification of said raw material, subjecting said alkali impregnated raw material to mechanical defibration and treating said defibrated raw material with an alkali solution of stronger chemical activity to effect deligni-~066697 fication thereof.
The method of the present invention has given sur-prisingly good results. Thus, impregnating shredded chips of Eucalyptus of about 2 by 2 mm section at 125C during 5 minutes with a mixture of green liquor and black liquor with a total alkali content of 8~ based on dry wood weight, raising the temperature in 15 secor.ds by direct injection of steam to 170C, defibrating the material at this temperature, adding in the defibration white liquor with 25% sulphidity containing 10%
active alkali based on dry wood and cooking the defibered mat-erial during 3 minutes, the following results have been obtained: -Screened yield: 60.1%
Tensil strength: 12,500 -Tear strength: 118 Tests also indicate that essentially the same results may be achieved without adding sodium sulphide to the process, -thus allowing for a sulphur-free high yield, high quality pulping process. This process adapts itself perfectly to the deligni-fication of fiberous raw material with oxygen in an alkali solution. Laboratory tests have been carried out with Eucalyptus wood and it i8 anticipated corresponding improvements will be achieved using any wood or other fiberous raw material as for example sugar cane bagasse and bamboo.
Due to the fact that the delignification i8 effected on defibered raw material, the process is independent of the - ~ density of this raw material. Thus, a heterogeneous raw material such as mixed hardwoods or a mixture of softwood and hardwood or a mixture of bamboo and wood of any kind will give a homogen-eous end product. The pieces of the raw material must not nec-essarily be in the form of normal chips, reduced to sticks of about 2 to 3 mm section. The chips of constant thickness as produced in a drum chipper are very well suited for the process.
_ 5 _ -.`; : `
- , . . . . : .: . .. .
1066~
The ideal thickness of the chips is about 2 mm. Length and width can vary within any practical limit. Normal sized chips as used in pulp mills may be used but with the disadvantage of not achieving a homogeneous impregnation and heating through the chips, resulting in increased reaction time and decreased yield and strength properties of the pulp.
Impregnation of the raw material with green liquor or any other slow acting alkali agent followed by cooking with a B fast acting alkali agent is/little advantage if not used in combination with defibering the raw material between impregnation and cooking, because only in this way the selective dissolving of lignin by the white liquor can take place as described above.
In addition to the advantages already described the process of the present invention results in less organic sub-stance per ton of pulp to be treated in the recovery system and thus higher capacity in terms of ton of pulp/day in existing plants or smaller and thus cheaper units in new plants. Only part - about 50% - of the green liquor will be transformed into white liquor in the causticizing plant, giving correspondingly higher capacity in existing installations or smaller new in-stallations. This also applies to the reburning plant for lime sludge .
'; ' ,~
~
. : '' :
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of manufacturing a chemical pulp from a fibrous raw material which comprises homogeneously impregnat-ing the fibrous raw material with an alkali solution of weaker chemical activity whereby to minimize delignification of said raw material, subjecting said alkali impregnated raw material to mechanical defibration and treating said defibrated raw material with an alkali solution of stronger chemical activity to effect delignification thereof.
2. A method as claimed in claim 1, in which the alkali solution of weaker chemical activity is a sodium carbonate solution.
3. A method as claimed in claim 2, in which the sodium carbonate solution contains sodium sulphide.
4. A method as claimed in claim 3, in which the alkali solution of weaker chemical activity is a green liquor.
5. A method as claimed in claim 1, in which the alkali solution of weaker chemical activity is a solution of hydrogen sulphide or polysulphide.
6. A method as claimed in claim 1, 2 or 3, in which the impregnation is effected at a temperature from 120-170°C.
7. A method as claimed in claim 1, 2 or 3, in which the impregnated raw material is defibrated at a temperature from 160-180°C.
8. A method as claimed in claim 1, 2 or 3, in which the defibrated raw material is cooked with sodium hydroxide solution to effect delignification thereof.
9. A method as claimed in claim 1, 2 or 3, in which the defibrated raw material is cooked with sodium hydroxide containing sodium sulphide to effect delignification thereof.
10. A method as claimed in claim 1, 2 or 3, in which the defibrated raw material is cooked with white liquor to effect delignification.
11. A method as claimed in claim 1, 2 or 3, in which the fibrous raw material is wood chips.
12. A method as claimed in claim 1, 2 or 3, in which the alkali solution of stronger chemical activity is added after defibration of the raw material.
13. A process of making cellulose or pulp for paper manufacture or chemical uses comprising a) subjecting shredded wood fibers in the form of chips or sticks to an impregnation with a relatively slow acting alkaline agent at a temperature of about 125° for a time of about 5 minutes with or without the addition of sodium sulphide so as to prevent damage to the fiber walls during the subsequent cooking step; b) then raising the temperature of the impregnated wood fibers by steam injection to about 170°C; c) then subjecting the fibers at the latter tempera-ture to a defiberization step, d) and after or during the defiber-ization step adding an alkaline agent that is fast acting relative to the alkaline agent used in step 1, with or without the addition of sodium sulphide, and subjecting the mass to cooking in said fast-acting alkaline agent during a time of about 2 to 5 minutes at said temperature of about 170°C so as to selectively dissolve the lignine of the defiberized mass, whereby a high yield of a pulp of high tensile strength and high tear strength is obtained.
14. The process of claim 13 wherein the shredded wood fibers in the form of chips or sticks submitted to said impregna-tion step have a size of between about 2 x 2 and 3 x 3 mm in cross section or have a constant thickness of about 2 mm.
15. The process of claim 13 wherein said impregnation is effected with a so-called green liquor or a mixture of the green liquor with used cooking liquor, so-called black liquor, and wherein the final cooking is effected with caustic soda with or without sodium sulphide, so-called white liquor.
16. The process of claim 15 wherein the total active alkali content of the said green liquor or mixture of said green liquor with black liquor is about 8% and that of the white liquor is about 10% based on the dry wood weight.
17. The process of claim 16 wherein the said white liquor has about 25% sulphidity.
18. The process of claim 13 wherein the alkaline agent used in the impregnating step is essentially sodium carbonate and wherein the alkaline agent used in the cooking liquor is essentially sodium hydroxide.
19. The process of claim 13 wherein the temperature of the impregnated mass is raised in about 15 seconds to said temperature of about 170°C.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| BR7505352 | 1975-08-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1066697A true CA1066697A (en) | 1979-11-20 |
Family
ID=3996454
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA259,578A Expired CA1066697A (en) | 1975-08-20 | 1976-08-20 | Method of producing cellulose |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5237802A (en) |
| CA (1) | CA1066697A (en) |
| FI (1) | FI762341A (en) |
| SE (1) | SE7609148L (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012007642A1 (en) | 2010-07-13 | 2012-01-19 | Olli Joutsimo | Improved method of processing chemical pulp |
| US11440214B2 (en) * | 2017-04-03 | 2022-09-13 | University Of Maryland, College Park | Flexible wood structures and devices, and methods for fabricating and use thereof |
| US11578894B2 (en) | 2017-06-09 | 2023-02-14 | University Of Maryland, College Park | Wood-based solar thermal devices, and methods for fabrication and use thereof |
| US11958209B2 (en) | 2017-09-15 | 2024-04-16 | University Of Maryland, College Park | Delignified wood materials, and methods for fabricating and use thereof |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3773610A (en) * | 1970-12-11 | 1973-11-20 | Bauer Bros Co | Pressurized system for pulp refining including pressurized double disk treatment |
| JPS4887101A (en) * | 1972-02-22 | 1973-11-16 |
-
1976
- 1976-08-17 SE SE7609148A patent/SE7609148L/en not_active Application Discontinuation
- 1976-08-17 FI FI762341A patent/FI762341A/fi not_active Application Discontinuation
- 1976-08-20 JP JP51098812A patent/JPS5237802A/en active Pending
- 1976-08-20 CA CA259,578A patent/CA1066697A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012007642A1 (en) | 2010-07-13 | 2012-01-19 | Olli Joutsimo | Improved method of processing chemical pulp |
| US9139955B2 (en) | 2010-07-13 | 2015-09-22 | Olli Joutsimo | Method of processing chemical pulp |
| US11440214B2 (en) * | 2017-04-03 | 2022-09-13 | University Of Maryland, College Park | Flexible wood structures and devices, and methods for fabricating and use thereof |
| US11578894B2 (en) | 2017-06-09 | 2023-02-14 | University Of Maryland, College Park | Wood-based solar thermal devices, and methods for fabrication and use thereof |
| US11958209B2 (en) | 2017-09-15 | 2024-04-16 | University Of Maryland, College Park | Delignified wood materials, and methods for fabricating and use thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| FI762341A (en) | 1977-02-21 |
| JPS5237802A (en) | 1977-03-24 |
| SE7609148L (en) | 1977-02-21 |
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