CA1064748A - Process of making pulp from lignocellulose containing material - Google Patents
Process of making pulp from lignocellulose containing materialInfo
- Publication number
- CA1064748A CA1064748A CA285,696A CA285696A CA1064748A CA 1064748 A CA1064748 A CA 1064748A CA 285696 A CA285696 A CA 285696A CA 1064748 A CA1064748 A CA 1064748A
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- CA
- Canada
- Prior art keywords
- pulp
- irradiation
- kwh
- steam
- temperature
- 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.)
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Abstract
PROCESS OF MAKING PULP FROM LIGNO-CELLULOSE CONTAINING MATERIAL
ABSTRACT OF THE DISCLOSURE
Method of making high yield pulp for papermaking with re-duced energy consumption, in which the pulp material, such as wood chips and other lignocellulose-containing material, is first heat-ed in an environment of steam to a temperature exceeding 120°C
and preferably higher than 140°C, under corresponding steam pres-sure, and then subjected to a first fiber separation step in a disc type defibrating apparatus under maintenance of substantially the same temperature and steam pressure. The thus defibrated pulp material is passed through an electron radiation apparatus under reduced pressure, where the initially separated fibers are sub-jected to irradiation with electrons to enhance the pulping pro-perties of the pulp material. Thereafter, the irradiated and in-itially defibrated pulp material is subjected to a second fiber separation step in a second defibrator, under lower temperature and pressure than in the first defibrating step, before it is dis-charged for further elective processing. The irradiation of the initially separated fibers should be in an amount sufficient to carry out the two defibrating steps at an energy consumption of less than 500 KWh per ton of pulp, and preferably between 100 KWh and 300 KWh.
ABSTRACT OF THE DISCLOSURE
Method of making high yield pulp for papermaking with re-duced energy consumption, in which the pulp material, such as wood chips and other lignocellulose-containing material, is first heat-ed in an environment of steam to a temperature exceeding 120°C
and preferably higher than 140°C, under corresponding steam pres-sure, and then subjected to a first fiber separation step in a disc type defibrating apparatus under maintenance of substantially the same temperature and steam pressure. The thus defibrated pulp material is passed through an electron radiation apparatus under reduced pressure, where the initially separated fibers are sub-jected to irradiation with electrons to enhance the pulping pro-perties of the pulp material. Thereafter, the irradiated and in-itially defibrated pulp material is subjected to a second fiber separation step in a second defibrator, under lower temperature and pressure than in the first defibrating step, before it is dis-charged for further elective processing. The irradiation of the initially separated fibers should be in an amount sufficient to carry out the two defibrating steps at an energy consumption of less than 500 KWh per ton of pulp, and preferably between 100 KWh and 300 KWh.
Description
FIELD OF THE INVENTION
-This invention relates to ~he making of pulp from ligno-cellulose containing material.
~ore particularly, this invention relates to a process of making pulp ~rom lignocellolose containing material which process comprises a step of preheating by steam of the material at a tem-perature exceeding 140C and a steam pressure corresponding there-to, a defibering step in a first grinding apparatus at substantlal-~: ly the same temperature and pressure as in the preheating step and at least one additional grinding step at lower temperature and ; pressure. ~
...~.
7~ 51 BACKGROUND OF THE INVENTION
... . _ _ .
~t the high temperature during the preheating step and also during the first grinding step, components of the lignocellulose containing material which have a relatively amorphous structure, especially hemicellulose and lignin, are weakened. Since the la~
mellae between the fibers consist of material of this kind, the fibers can be uncovered and separated from one another substan-tially undamaged and with low input of energy under these con-ditions.
THE PRIOR ~RT
The demand for energy in a one step process for uncovering the fibers by means of a preheating step followed by a defibering step in a grinding apparatus equipped with grinding discs rotatable rel-atively to one another is in a known process as low as from 250 KWh to 300 KWh. The obtained pulp is excellently suited for manufacture ~` of, e.g., fiber board, but has proved not to be suited for manufac-ture of paper possessing required strength. The main reason for this limitation of the usability of the pulp resides primarily in the feature that the strongly cross-linked polymers result in too stiff fibers and fibers which only with difficulty can be rendered flaxible and fibrillated to the degree required to impart to the paper good strength qualities. To arrive at least near to the de-sired properties of the final product in this respect, the pulp must be passed through a greater number of refining steps, ~ith a con-sequent very high input of energy, which energy consumption is in-tolerable in practice.
More recently, the so-called thermomechanical method of pulp-making has been developed. This method implies that the starting material, such as wood chips, prior to defibration and refining is heated to a slightly lower temperature, such as between 120C and 130C, at which temperature the softening effect mentioned above is achieved only partiall~. On the other hand, the thermomechan-ical method yields a fibrous product excellently suited for man-~
74~
ufacture of paper by rendering possi~le a highly advanced fib-rillation and plasticization of the fibers, but it still requires a considerable amount o~ energy, namely,2,QOO Kl~h or slightly less, per ton of pulp.
Due to the action of the high temperature, exceeding 140C, and usually of about 170C, applied in the first-mentioned method applied in the preheating step and the first grinding step, the pulp becomes darkly discoloured. This darkening can, however, be eliminatPd, at least to a major part, by addition of either plas-lQ ticizers to the starting material or bleaching agents to the ma-`~ terial under treatment. In the first-mentioned case, the defi-brating step, i.e., the fiber-separating step, can be carried out at a lower temp~rature than that usually employed, which reduces the darkening effect.
MAIN OBJECT OF ~HE INVENTION
With the above-stated drawbacks in mind, one main object of the invention is to provide a process for making.pulp with a yield exceeding 90%, which pulp acquires properties desirable for paper-making by an input of energy radically lower than that required in present commercial processes for production of mechanical pulp, including the thermomechanical method.
SUMMARY OF THE INVENTION
The present invention is an improvement over the processgenerally described hereinbefor~, with high preheating temperature, i.e., a temperature exceeding 140C, prior to the first grinding step carried out at substantially the same temperature, and is characterized primarily by the feature that the pulp, in order to acquire good paper-forming properties,.aftex:the.initial defibrat.-.
ing step is subjected to another kind of treatment than grinding, at low input of energy, in order to break up cohesive links in the unravelled fibers~ Preferably, this treatment of another kind is an irradiation with electrons.
In accordance with the invention, it has proved to be pos-~, ~)64~7~L35 sible with a low input of energy, namely, less than 500 KWh per ton of pulp, and most conveniently, between 100 KWh and 300 KWh per ton of pulp, in a subsequent second grinding step to obtain de-sired properties, primarily increased flexibility combined with retained high mechanical strength of the fibers. This second grinding step is carried out in the same manner as the first one, preferably in a grinding apparatus of the disc type. The total in-put of energy is thus reduced, when compared with the thermomechan-ical method, to less than one-half or down to about one-quarter.
As upper limit for the preheating temperature, 180C to 190C
may be fixed, the temperature preferably being kept within the range from 150~C to 170C. The yield obtained by the method of the invention is about 95%, i.e., of the same order of magnitude as obtainable with the conventional thermomechanical method.
The irradiation with electrons is carried out by exposing the pulp with a dry content of between 10% and 90% for a period of time ranging between 1 second and 20 seconds to irradiation between the electrodes of a unit intended for emission of high energy elec-trons. The dosage for the irradiation with electrons is to be kept within the range from 0.1 megarad to 0.5 megarad.
The darkening of the fiber pulp caused by the high temper- , ature maintained in the preheating step and the first grinding step can be counteracted and even eliminated in known manner by ad-dition of plasticizers or bleaching agents. To this end, and also to assist in the plasticization of the amorphous polymers of the ; starting material, it is advantageous to add between 0.1% and 0.5%
of sodium hydrosulfite in the thermic pretreatment.
The treatment ~f the fibrous material prior to, and after, the irradiation with electrons can be performed in a plant of known construction, as is disclosed in, e.g., the U.S. Patent Specifi-cation No. 3,388,037. The startin~ material, such as, e.g., wood chips, is introduced by a cell feeder or a screw feeder into a pre-heater wherein the chips are preheated rapidly by means of steam 1~6~74~
to a temperature exceeding 140C, such as 170C. Thereupon, the chips at this temperature and under coresponding steam pressure are fed into a disc-equipped grinding apparatus where they are subjected to a first grinding step. The total dwell time at the temperature prevailing in the preheater and the defibering appar-atus shall be short, and thus, be 5 minutes at the utmost. Al-though, by this treatment, the fibers are separated from one an-other to a substantial degree, the pulp still is not suited to be ground finally for the purpose of making paper. This is accom-plished by exposing the defibrated fiber pulp to irradiation by high energy electrons in an apparatus unit comprising a high volt-age accelerator, ray focussing means, means for conveying the radi-ated material and means of radiation protection. The apparatus unit may be of the type marketed under the trademark "Dynamitron"
and manufactured by Radiation Dynamics of New York, N. Y., U.S.A.
Between the electrodes of the unit, a DC voltage of 1.5 megavolt is generated. For the passage through the apparatus unit for irradiation with electrons, the pressure and tempPrature of the pulp is lowered, the reduction of the pressure preferably being down to atmospheric pressure. By the irradiation with electrons, the links in the fibers are broken up and the plasticization andl, uncovering or separation of the fibrils in the continued grind-ing treatment is rendered easier.
Thereafter, the pulp is subjected to further grinding in a second step carried out in a disc refiner at a lower pressure and temperature than in the first grinding step, such as at room temperature.
In order to counteract darkening of the fibrous material, a plasticizer or bleaching agent, such as sodlum hydrosulfite, is added to the material at least in the first grinding step.
D~SCRIPTION OF ~ SPECIFIC E ~PI.E
Chips prepared from coniferous wood are introduced into a preheater while having a dry content of about 40%. In the pre-,~.
~o~
heater, the chips are treated wit~ steam having a temperature of about 170C and being under a corresponding high pressure. ThP
preheated chips are fed into a disc-equipped grinding mill wherein the same temperature and pressure are maintained and wherein they are subjected to a grinding treatment for 2 minutes. During the passage through the disc refiner, 250 KWh are supplied per ton of material, the wood chips thereby being disintegrated into substan-~;; tially individual fibers with a yield of about 96V/o. The defi-brated material is passed through an electron radiation apparatus unit of the type "Dynamitron" identified hereinbefore, while sup-ported on a conveyor belt. In this apparatus unit, the fibrous ~: material has a lower dry content, viz. of about 20%, and the ir-radiation with electrons suitably is dimensioned so as to reach a total dosing of 0.15 megarad. Thereupon, the material is sub-jected to a second grinding treatment in a disc refiner. The ma-terial here has a still lower dry content, such as of about 10%, and the input of energy in this step is about 100 KWh per ton of pulp. The total yield of pulp from wood is about 95%.
The properties of the finished pulp are tested by forming standardized laboratory sheets having a surface weight of 70gs per square meter, the tensile strength of which sheets is compar-ed with that of sheets formed from non-irradiated, but otherwise similarly treated, pulp in a tension testing machine at a relative air moisture of 50% and a temperature of 20C. The following values have been ascertained:
Tensile strength for paper sh~eets meters Paper manufactured from pulp pro-duced as described above, but without irradiation with electrons 100 Paper manufactured from pulp produced according to the invention 4,900 It is evident that paper made from pulp produced by the pro cess according to the invention has a tensile strength of the same . -6-~ 6 ~7 ~ ~
standard as paper made from the best mechanical pulps available in the market. However, the total input of energy for p~oducing the pulp according to the example set forth above is less than 400 KWh per ton of pulp, to be compared with those 1,500 KWh to
-This invention relates to ~he making of pulp from ligno-cellulose containing material.
~ore particularly, this invention relates to a process of making pulp ~rom lignocellolose containing material which process comprises a step of preheating by steam of the material at a tem-perature exceeding 140C and a steam pressure corresponding there-to, a defibering step in a first grinding apparatus at substantlal-~: ly the same temperature and pressure as in the preheating step and at least one additional grinding step at lower temperature and ; pressure. ~
...~.
7~ 51 BACKGROUND OF THE INVENTION
... . _ _ .
~t the high temperature during the preheating step and also during the first grinding step, components of the lignocellulose containing material which have a relatively amorphous structure, especially hemicellulose and lignin, are weakened. Since the la~
mellae between the fibers consist of material of this kind, the fibers can be uncovered and separated from one another substan-tially undamaged and with low input of energy under these con-ditions.
THE PRIOR ~RT
The demand for energy in a one step process for uncovering the fibers by means of a preheating step followed by a defibering step in a grinding apparatus equipped with grinding discs rotatable rel-atively to one another is in a known process as low as from 250 KWh to 300 KWh. The obtained pulp is excellently suited for manufacture ~` of, e.g., fiber board, but has proved not to be suited for manufac-ture of paper possessing required strength. The main reason for this limitation of the usability of the pulp resides primarily in the feature that the strongly cross-linked polymers result in too stiff fibers and fibers which only with difficulty can be rendered flaxible and fibrillated to the degree required to impart to the paper good strength qualities. To arrive at least near to the de-sired properties of the final product in this respect, the pulp must be passed through a greater number of refining steps, ~ith a con-sequent very high input of energy, which energy consumption is in-tolerable in practice.
More recently, the so-called thermomechanical method of pulp-making has been developed. This method implies that the starting material, such as wood chips, prior to defibration and refining is heated to a slightly lower temperature, such as between 120C and 130C, at which temperature the softening effect mentioned above is achieved only partiall~. On the other hand, the thermomechan-ical method yields a fibrous product excellently suited for man-~
74~
ufacture of paper by rendering possi~le a highly advanced fib-rillation and plasticization of the fibers, but it still requires a considerable amount o~ energy, namely,2,QOO Kl~h or slightly less, per ton of pulp.
Due to the action of the high temperature, exceeding 140C, and usually of about 170C, applied in the first-mentioned method applied in the preheating step and the first grinding step, the pulp becomes darkly discoloured. This darkening can, however, be eliminatPd, at least to a major part, by addition of either plas-lQ ticizers to the starting material or bleaching agents to the ma-`~ terial under treatment. In the first-mentioned case, the defi-brating step, i.e., the fiber-separating step, can be carried out at a lower temp~rature than that usually employed, which reduces the darkening effect.
MAIN OBJECT OF ~HE INVENTION
With the above-stated drawbacks in mind, one main object of the invention is to provide a process for making.pulp with a yield exceeding 90%, which pulp acquires properties desirable for paper-making by an input of energy radically lower than that required in present commercial processes for production of mechanical pulp, including the thermomechanical method.
SUMMARY OF THE INVENTION
The present invention is an improvement over the processgenerally described hereinbefor~, with high preheating temperature, i.e., a temperature exceeding 140C, prior to the first grinding step carried out at substantially the same temperature, and is characterized primarily by the feature that the pulp, in order to acquire good paper-forming properties,.aftex:the.initial defibrat.-.
ing step is subjected to another kind of treatment than grinding, at low input of energy, in order to break up cohesive links in the unravelled fibers~ Preferably, this treatment of another kind is an irradiation with electrons.
In accordance with the invention, it has proved to be pos-~, ~)64~7~L35 sible with a low input of energy, namely, less than 500 KWh per ton of pulp, and most conveniently, between 100 KWh and 300 KWh per ton of pulp, in a subsequent second grinding step to obtain de-sired properties, primarily increased flexibility combined with retained high mechanical strength of the fibers. This second grinding step is carried out in the same manner as the first one, preferably in a grinding apparatus of the disc type. The total in-put of energy is thus reduced, when compared with the thermomechan-ical method, to less than one-half or down to about one-quarter.
As upper limit for the preheating temperature, 180C to 190C
may be fixed, the temperature preferably being kept within the range from 150~C to 170C. The yield obtained by the method of the invention is about 95%, i.e., of the same order of magnitude as obtainable with the conventional thermomechanical method.
The irradiation with electrons is carried out by exposing the pulp with a dry content of between 10% and 90% for a period of time ranging between 1 second and 20 seconds to irradiation between the electrodes of a unit intended for emission of high energy elec-trons. The dosage for the irradiation with electrons is to be kept within the range from 0.1 megarad to 0.5 megarad.
The darkening of the fiber pulp caused by the high temper- , ature maintained in the preheating step and the first grinding step can be counteracted and even eliminated in known manner by ad-dition of plasticizers or bleaching agents. To this end, and also to assist in the plasticization of the amorphous polymers of the ; starting material, it is advantageous to add between 0.1% and 0.5%
of sodium hydrosulfite in the thermic pretreatment.
The treatment ~f the fibrous material prior to, and after, the irradiation with electrons can be performed in a plant of known construction, as is disclosed in, e.g., the U.S. Patent Specifi-cation No. 3,388,037. The startin~ material, such as, e.g., wood chips, is introduced by a cell feeder or a screw feeder into a pre-heater wherein the chips are preheated rapidly by means of steam 1~6~74~
to a temperature exceeding 140C, such as 170C. Thereupon, the chips at this temperature and under coresponding steam pressure are fed into a disc-equipped grinding apparatus where they are subjected to a first grinding step. The total dwell time at the temperature prevailing in the preheater and the defibering appar-atus shall be short, and thus, be 5 minutes at the utmost. Al-though, by this treatment, the fibers are separated from one an-other to a substantial degree, the pulp still is not suited to be ground finally for the purpose of making paper. This is accom-plished by exposing the defibrated fiber pulp to irradiation by high energy electrons in an apparatus unit comprising a high volt-age accelerator, ray focussing means, means for conveying the radi-ated material and means of radiation protection. The apparatus unit may be of the type marketed under the trademark "Dynamitron"
and manufactured by Radiation Dynamics of New York, N. Y., U.S.A.
Between the electrodes of the unit, a DC voltage of 1.5 megavolt is generated. For the passage through the apparatus unit for irradiation with electrons, the pressure and tempPrature of the pulp is lowered, the reduction of the pressure preferably being down to atmospheric pressure. By the irradiation with electrons, the links in the fibers are broken up and the plasticization andl, uncovering or separation of the fibrils in the continued grind-ing treatment is rendered easier.
Thereafter, the pulp is subjected to further grinding in a second step carried out in a disc refiner at a lower pressure and temperature than in the first grinding step, such as at room temperature.
In order to counteract darkening of the fibrous material, a plasticizer or bleaching agent, such as sodlum hydrosulfite, is added to the material at least in the first grinding step.
D~SCRIPTION OF ~ SPECIFIC E ~PI.E
Chips prepared from coniferous wood are introduced into a preheater while having a dry content of about 40%. In the pre-,~.
~o~
heater, the chips are treated wit~ steam having a temperature of about 170C and being under a corresponding high pressure. ThP
preheated chips are fed into a disc-equipped grinding mill wherein the same temperature and pressure are maintained and wherein they are subjected to a grinding treatment for 2 minutes. During the passage through the disc refiner, 250 KWh are supplied per ton of material, the wood chips thereby being disintegrated into substan-~;; tially individual fibers with a yield of about 96V/o. The defi-brated material is passed through an electron radiation apparatus unit of the type "Dynamitron" identified hereinbefore, while sup-ported on a conveyor belt. In this apparatus unit, the fibrous ~: material has a lower dry content, viz. of about 20%, and the ir-radiation with electrons suitably is dimensioned so as to reach a total dosing of 0.15 megarad. Thereupon, the material is sub-jected to a second grinding treatment in a disc refiner. The ma-terial here has a still lower dry content, such as of about 10%, and the input of energy in this step is about 100 KWh per ton of pulp. The total yield of pulp from wood is about 95%.
The properties of the finished pulp are tested by forming standardized laboratory sheets having a surface weight of 70gs per square meter, the tensile strength of which sheets is compar-ed with that of sheets formed from non-irradiated, but otherwise similarly treated, pulp in a tension testing machine at a relative air moisture of 50% and a temperature of 20C. The following values have been ascertained:
Tensile strength for paper sh~eets meters Paper manufactured from pulp pro-duced as described above, but without irradiation with electrons 100 Paper manufactured from pulp produced according to the invention 4,900 It is evident that paper made from pulp produced by the pro cess according to the invention has a tensile strength of the same . -6-~ 6 ~7 ~ ~
standard as paper made from the best mechanical pulps available in the market. However, the total input of energy for p~oducing the pulp according to the example set forth above is less than 400 KWh per ton of pulp, to be compared with those 1,500 KWh to
2,000 KWh per ton..required.for mechanical pulp produced according to hitherto available methods, thereinto included the thermomechan-ical method.
,:~
:~
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:~
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Claims (2)
PROPERTY OF PRIVILEGE IS CLAIMED, ARE DEFINED AS FOLLOWS:
1. In the process of continuously producing high yield mechanical pulp from lignocellulose-containing material which is first heated in an environment of steam at a temperature above 120°C and at a corresponding superatmospheric steam pressure and then passed to a first disc-type defibrator for initial fiber separation without substantial reduction in temperature and pres-sure and thereafter passed to a second disc-type defibrator for further fiber separation and fibrillation under reduced temper-ature and pressure, the improvement enhancing the pulping proper-ties of the pulp material with minimized energy consumption, com-prising: subjecting the initially separated fibers before being passed to the second defibrator to irradiation with electrons in an amount and for a period of time sufficient to reduce the ener-gy requirement for the second step to an amount not exceeding that of the first step so as to substantially equalize the energy re-quirements for the two defibration steps to a predetermined value calculated in accordance with the desired pulp qualities.
2. The process according to Claim 1, in which the initially separated fibers are subjected to irradiation in an amount and for a period of time sufficient to reduce the total energy re-quirement for the two steps to less than 500 KWh per ton of pulp.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7609950A SE406711B (en) | 1975-09-10 | 1976-09-09 | TOY BUILDING KIT |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1064748A true CA1064748A (en) | 1979-10-23 |
Family
ID=20328842
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA285,696A Expired CA1064748A (en) | 1976-09-09 | 1977-08-29 | Process of making pulp from lignocellulose containing material |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1064748A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102009057208A1 (en) | 2009-11-27 | 2011-06-01 | Technische Universität Dresden | Process for the production of lignocellulosic paper pulps and papers, cartons and boards derived therefrom |
-
1977
- 1977-08-29 CA CA285,696A patent/CA1064748A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102009057208A1 (en) | 2009-11-27 | 2011-06-01 | Technische Universität Dresden | Process for the production of lignocellulosic paper pulps and papers, cartons and boards derived therefrom |
| WO2011063800A2 (en) | 2009-11-27 | 2011-06-03 | Technische Universität Dresden | Method for producing lignocellulosic paper pulps and papers, cardboards, and paperboards obtained therefrom |
| WO2011063800A3 (en) * | 2009-11-27 | 2011-07-21 | Technische Universität Dresden | Method for producing lignocellulosic paper pulps and papers, cardboards, and paperboards obtained therefrom |
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