JPH0114358B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for reducing the resin content of cellulose pulps during the production of these pulps from lignocellulosic materials. Here, cellulose pulp preferably means chemical pulp, that is, pulp produced by a chemical cooking method. The invention is primarily applicable to the production of sulfite pulp, but the production of kraft pulp from hardwoods such as birch is also an important field of application of the invention. The invention can also be implemented in the production of high yield pulps such as semi-chemical pulps, thermomechanical pulps and mechanical pulps. These pulps are primarily used for paper making, but can also be used to make sanitary napkins, and high quality pulps can also be used to make cellulose derivatives. PRIOR ART The raw material for the production of cellulose pulp is lignocellulose, for example in the form of wood, which always contains more or less a resin content. It is desirable to remove as much of this resin as possible during the pulp manufacturing process so that the treated pulp has a low resin content. High resin content in the final pulp occurs when the pulp is used (e.g. in paper production)
This causes various problems and impairs the quality of the final product. In addition, the presence of resin complicates pulp production itself. Therefore, when producing pulp by the sulfite process, the wood is always stored for a certain period of time before it is introduced into the digester and digested into cellulose pulp. During this storage, called seasoning, changes occur in the physical properties of the resin, the amount of resin in the wood decreases somewhat, and the resin itself changes so that it is more easily soluble during the pulping process. Storage of wood can be carried out in various ways. For example, wood in the form of logs is first stored underwater (suspended and pulled), and then logs in the form of bundles are stored on land in a timber yard. After approximately one year of storage, the logs are transported to a pulp mill for cutting into chips and other processing to make pulp. Another method is to cut the logs into chips already on arrival at the pulp mill and store the chips in piles. If the wood is treated in this way, the storage time will be reduced by approximately 3
It can be shortened to months. Processing of any storage method always means costs, resulting in the loss of a certain amount of wood coupled with a loss of considerable amounts of money. Despite storage, the wood still contains a significant amount of resin, although the shape is slightly altered compared to the resin in new wood. Most of the remaining resin content is removed at various stages of the pulp manufacturing process, but removing all the resin from the pulp is difficult and especially expensive. The final pulp therefore almost invariably contains some amount of resin. Some of the resin also dissolves during wood cooking and is removed when the pulp is washed and screened. Final adjustment of the resin content of the pulp is carried out in the bleaching department. It is primarily in the alkaline stage of the bleach series that the resin is removed. However, it is also possible and not uncommon for final adjustments to be made at the chlorine dioxide stage. At the sulfite factory, chlorine (C), alkali (E),
Hypochlorite (H) and chlorine dioxide (D) bleaching series,
That is, C-E-H-D- is normally used. By varying the amount of alkali, usually sodium hydroxide, in the E stage, more or less resin can be extracted. Sodium hydroxide and a dispersant are often used in the E stage to keep the resin in a decomposed form (so that it does not clump) so that it can be washed out of the pulp as much as possible in the washing process after the E stage. added. Final adjustment of the resin content is usually carried out in the D stage, ie by varying the amount of chlorine dioxide added. The resin is separated from the pulp in a washing step after the D stage. When resin problems occur at the plant (eg, foaming, clogging), it may be necessary to reduce the amount of C-stage chlorine and correspondingly increase the amount of chlorine dioxide. As is well known to those skilled in the art, chlorination of the resin means that it becomes more difficult to handle. A major disadvantage of using large amounts of chlorine dioxide to treat resin problems is the high cost of this chemical. When producing pulp by the kraft method,
Wood is not stored in any way. For example, to overcome resin problems in the production of birch kraft pulp, careful debarking of logs is important. This is because the bark, especially the cambium between the bark and the wood, contains a large amount of resin. Similar to sulfite cooking, resin dissolution occurs in kraft cooking. Tall oil is added into the digester to keep the resin in dispersed form (to avoid agglomeration) during cooking. The resin extracted during cooking is separated from the pulp in a subsequent washing step and conveyed together with the black liquor to an evaporator and then to a soda recovery furnace. In the production of kraft pulp, the resin content cannot be adjusted by varying the amount of alkali added in the alkaline stage of the bleaching series.
Rather, the final adjustment of the resin content is completely limited to the expensive bleaching agent chlorine dioxide. In the production of birch kraft pulp, therefore, to overcome the resin problem, one must either make a high investment in high quality debarking equipment or add large amounts of high bleaching agent chlorine dioxide in the bleaching section. Or you need both. Even with these costly measures, it is difficult to reach the desired low resin content of the final pulp. Pulps with low resin content are, as is well known, highly desirable in the market. In addition to the methods described above, the resin content of the cellulose pulp can be reduced to some extent by adding various surfactants, so-called wetting agents, at various points in the manufacturing operation. The method described so far is one of the most common methods implemented to overcome resin problems in the production of cellulose pulp. More recently, a method for reducing the resin content in cellulose pulp has been routinely used in the cellulose industry. Lignocellulosic materials can be separated (freed) of fibers,
It is subjected to washing, optionally screening, and optionally delignification bleaching. A feature of the new method is that it is subjected to chemical-mechanical treatment at the point in the cellulose pulp manufacturing process. Cellulose pulp is adjusted to a concentration of 15 to 35% and per kg of water accompanying the pulp.
2 to 17 g of alkali, calculated as NaOH, are added. The pulp is then processed at 8 to 100 kWh per pulp in equipment suitable for high concentration processing with screws that can rotate with respect to each other.
It is preferably subjected to mild mechanical treatment at an energy input of 10 to 75 kWh. Finally, the cellulose pulp is allowed to react with the added chemicals in a separate container for 0.1 to 5 hours at a substantially unchanged pulp concentration. After treatment intended to reduce the resin content of the cellulosic pulp, the pulp is usually transported to further processing stages in a bleaching plant in order to obtain a final brightness, usually greater than 90% ISO. It is also possible to complete the production of pulp with the above-mentioned treatment. This means producing unbleached or slightly bleached pulp. The aforementioned method is effective even when fresh wood is sent to the cooking department for cooking and fiber separation.
It has indeed been shown that pulp with the desired (low) resin content can be successfully produced. Other pulp properties such as purity are also improved when using this new method. For more details on this method, please refer to the patent application filed in 1983.
118245 (Japanese Unexamined Patent Publication No. 56-43496). DESCRIPTION OF THE INVENTION Technical Problem When using the method according to the Swedish patent application 7907557-8 for the production of unbleached or slightly bleached cellulose pulp, it has been found that the whiteness of the pulp is not at the same level as the high quality with respect to the resin content. Indicated. Solution The present invention solves this problem and the lignocellulosic material is subjected to fiber separation, washing, optional screening and optional delignification bleaching and in the form of a pulp with a pulp concentration of 15 to 35%, preferably 19 to 29%, and alkali-containing chemicals are added, after which the pulp is heated at 8 to 100 kWh per pulp, in an apparatus with screws rotating with respect to each other.
The lignosine is subjected to a mild mechanical treatment, preferably with an energy input of 10 to 75 kWh per pulp, and then reacted in a separate vessel with the added chemicals at a substantially unchanged pulp concentration for 0.1 to 5 hours. A process for reducing the resin content in the production of cellulose pulp from cellulosic material, characterized in that the addition of chemicals consists of an oxidizing bleach and an alkali of from 0.5 to 17 g NaOH calculated as NaOH per kg water present. The present invention relates to the method. The treatment according to the invention is carried out after the lignocellulosic material has been digested to cellulose pulp with cooking chemicals in a digester and separated from the cooking waste in a washing section. When the pulp leaves the washing section, it typically has a consistency of 4 to 6%. Before the pulp is subjected to treatment according to the invention, it is usually screened. Before screening, the pulp is diluted to have a concentration of 0.5 to 3% during screening. In special cases, it may be appropriate for the pulp to be subjected to a mild delignification bleaching with certain bleaching agents, such as chlorine and/or chlorine dioxide, before being subjected to the treatment according to the invention. According to the invention, the starting pulp is dewatered in one or more stages so as to obtain a consistency of 15 to 35%, preferably 19 to 20%. This concentration of the pulp is usually carried out in one stage, and suitable dewatering devices are drum washers, belt washers, roll presses and screw presses. Whether this enrichment is carried out in one stage or more (e.g. two stages) depends on whether the method of the invention is applied to some extent in existing equipment or whether the method is applied in entirely new or refurbished equipment. Depends on. In the existing equipment, it is installed after the screening section, and in the screening section, the normal pulp concentration of 0.5 to 3% is processed at 10 to 13%.
Usually have a drum watcher or thickener that increases to %. However, drum washers do not need to have such dehydration ability;
A very simple drum washer to increase the pulp consistency to 4% or more is sufficient. After passing through a drum washer or thickener, the pulp is conveyed to a device where final dewatering to a pulp consistency of 15 to 35% takes place. A preferred device is a screw press. To facilitate dehydration of the pulp, the PH value of the contained pulp can be adjusted to between 7 and 9 by adding alkali. After the dewatering stage, alkaline and oxidizing bleaches are added to the pulp. The amount of alkali added to the pulp is of utmost importance, as the amount of alkali, calculated as NaOH, is the amount of water present in the pulp suspension.
per kg of water or, if there is a question of its presence as a suspension, per kg of water accompanying the pulp, from 0.5 to
The amount added is adjusted to 17g. Sodium hydroxide is preferred as the alkali, but it is also possible to add other alkalis such as sodium hydroxide, oxidized white liquor, green liquor, and sodium carbonate alone or in mixtures thereof. Among oxidative bleaches, peroxide bleaches are preferred, and hydrogen peroxide is particularly preferred. However, even hypochlorite bleaches such as sodium hypochlorite can be used advantageously. Other oxidizing bleaches can also be considered. The amount of oxidizing bleach added is between 0.2 and 22 g of bleach per kg of water present, preferably 0.3
It is adjusted so that it is between 11g and 11g. In some cases it is advantageous to add other chemicals to the pulp, such as surfactants (wetting agents) and complexing agents, in addition to alkaline and oxidative bleaching agents. Thereafter, in an apparatus suitable for type concentration treatment with screws rotating with respect to each other, the energy input is between 8 and 100 kWh per pulpon;
The pulp is subjected to mild mechanical treatment, preferably at conditions of 10 to 75 kWh. Suitable devices for such treatments are screw defibrators, and the screw defibrator sold by MoDoMeKan AB under the name FROTAPULPER is particularly suitable. This screw defibrator basically consists of two rotating screws arranged parallel to each other in a housing with an inlet and an outlet. The screw is provided with screw stages having indentations on the periphery of at least some of the stages of the screw for engaging each other for the purpose of kneading the supplied material and forming teeth between the indentations. Such a screw defibrator is described in US Pat. No. 3,064,908. The pulp mixed with chemicals is subjected to shearing and kneading forces in the form of pulsating pressure loads in this screw defibrator. This treatment results in highly effective chemical impregnation of the pulp. The processing is mild with respect to pulp fibers, as they are not shortened (as is the case with beating or milling) or otherwise adversely affected. Processing in screw defibrators is usually carried out at atmospheric pressure, but
It can also be carried out at overpressures of up to 500 kPa. During mechanical kneading, the temperature of the pulp increases. This is because 60% of the input energy is converted into heat. The greater the energy input, the greater the temperature rise during operation. For reference, in the case of pulpers used to slush (unthaw) paper or pulp, typically at concentrations below 5%, the energy input per ton of pulp is typically less than 8 kWh, and for refiners, the energy input is typically less than 8 kWh per ton of pulp. Requires energy input. After this mild mechanical treatment, the pulp is transferred to a column or via suitable equipment such as a pump, screw feeder or belt conveyor for subsequent reaction with added chemicals (mainly alkalis) at the desired temperature. Transported in similar containers. The residence time of the pulp at this stage can vary between 6 minutes and 5 hours. The pulp is then washed in a known washing device and the resin extracted from the pulp is removed from the pulp. According to a preferred embodiment of the invention, short residence times are applied between the dewatering stage and the mild mechanical treatment. This short residence time is preferably ensured by transporting the pulp in a screw feeder. This residence time should be between 2 and 10 seconds. In addition to using a screw feeder, it can also be passed through a chemical mixer, which is a device used to mix chemicals into the pulp. In the processing of some pulps, the reaction temperature of the mild mechanical treatment of the pulp and the temperature of its subsequent reaction with added chemicals in the retention column may be adjusted by kneading and shearing operations to achieve the desired resin removal. It is necessary to raise the temperature above the temperature increase caused by. In such cases steam is added to the pulp and the addition of steam must be carried out during a short residence time. Addition of chemicals and steam to the pulp reduces pulp consistency. However, the pulp consistency should not be less than 15% when the pulp is subjected to mild mechanical treatment. After the pulp has been treated according to the present invention and washed to remove dissolved resin from the pulp, it can be transported directly to drying or to final production, such as the production of paper of various qualities. As a result, the method according to the invention can be applied primarily to unbleached pulps or to slightly bleached cellulose pulps. However, the method according to the invention is also perfectly possible to be applied to pulps bleached to various degrees, including bleaching to brightness levels of 90% ISO or higher. Effect Cellulose pulp is subjected to the treatment according to the present invention,
And by adjusting the chemical loading, temperature and energy input, it is possible to effectively adjust the resin content and brightness of the final pulp to the desired level. Regarding the resin content of pulp, the first
with an increase in temperature and an increase in energy input,
They lead to increased dissolution of resin from the pulp. Increasing the amount of alkali added does not have as great an effect on resin dissolution as the parameters mentioned above. For certain pulps, there is an optimum amount of alkali added. Additions above this amount have little or no effect on resin dissolution. Such excessive addition of alkali can adversely affect other pulp qualities.
Regarding the brightness of the pulp, the amount of oxidizing bleach added is primary and determines the level of brightness obtained. The invention can be utilized in a variety of ways. In the sulfite mill it has been found that the invention eliminates wood storage and makes it possible to bring new wood directly into the mill. As a result, the cost of producing sulfite pulp is considerably reduced, even including the cost of the equipment required for the method of the invention. Even if the wood reserves are kept intact in the sulfite mill, the method of the present invention is of great value because it allows the resin content of the final pulp to be adjusted in a completely different and better way than was previously possible. In a kraft mill, the invention makes it possible to produce, for example, birch kraft pulp with an average low resin content, which was not necessarily possible before. Furthermore, in the production of such pulps, it is possible to reduce the need for debarking of birch wood and to reduce the addition of the expensive chemical chlorine dioxide. This is also advantageous from the standpoint of environmental pollution. The effects of the method of the present invention are also shown in the Examples below. DESCRIPTION OF THE DRAWINGS FIG. 1 shows a suitable apparatus for a preferred embodiment of the method of the invention. BEST MODE FOR CARRYING OUT THE INVENTION Several tests and comparative tests according to the present invention were conducted. The method of conducting these tests and the results obtained are shown in the following implementation. Example 1 Screened spruce sulfite pulp of paper pulp grade was treated in accordance with the present invention using the apparatus shown in FIG. The properties of screened spruce sulfite pulp determined by the SCAN test method are shown in Table 1.

[Table] R ₁₈ above means the insoluble portion of the pulp in 18% NaOH solution. This screened pulp, having a temperature of 62° C., was sent via conduit 1 to screw press 2, where it was dewatered to a consistency of 29.5%. The forced water was removed through conduit 3. At the outlet of the screw press 2, alkali in the form of NaOH was added to the pulp in an amount of 1%, calculated on the bone-dry pulp. This addition is per Kg of water present
The amount of alkali was 4.2g NaOH. The alkali was stored as an aqueous solution in container 4 and sent to screw press 2 through conduits 5 and 6.
From the screw press 2 the pulp was sent through a conduit 7 to a screw feeder 8. The pulp is produced by Screw Feeder 8 by MoDoMekan AB
It was sent to Screw Defibrator 9, a type sold under the name FROTAPULPER. Immediately before the screw defibrator 9, hydrogen peroxide H ₂ O ₂ was added to the pulp in an amount of 0.21%, calculated on the bone-dry pulp. This addition amounted to 0.9 g H ₂ O ₂ per kg of water present.
Hydrogen peroxide in the form of an aqueous solution is stored in a container 10;
It was then sent to the pulp through conduits 11 and 12. In a screw defibrator 9, the pulp was subjected to a kneading and shearing process corresponding to an energy input of 28 kWh per pulpton. As a result, the pulp temperature rose to 69°C. The pulp was then allowed to fall by gravity through a vertical shaft and conduit 13 into column 14. In column 14, the reaction between the pulp and the chemicals NaOH and H ₂ O ₂ was carried out to completion. After 120 minutes, take a sample of the pulp, then wash and dry the sample.
analyzed. The analysis results are shown in Table 2. The above test was repeated except that no hydrogen peroxide was added to the pulp (O-test). This pulp was also washed, dried and analyzed.
The results of the analysis are shown in Table 2.

TABLE From the above table it is clear that the invention provides a higher degree of whiteness compared to the O-test. Furthermore, the present invention lowered the pulp number while maintaining the same viscosity compared to the O-test. The resin content is very low for both pulps. Example 2 Simultaneously with the above tests conducted on a large scale, samples of paper grade screened spruce sulfite pulp were taken for laboratory testing. In these tests, the chemicals NaOH and
NaOH + H ₂ O ₂ were each added to the pulp in a conventional manner. In test 1, a certain amount of pulp is sent to a processing vessel and kept in a water bath at 69°C, and 1% NaOH, calculated for bone-dry pulp, is transferred into the pulp by a propeller agitator in the form of an aqueous solution. mixed. This addition meant that the amount of NaOH was 1.4 g per kg of water present. The pulp was allowed to react with sodium hydroxide for 120 minutes, after which the pulp was washed, dried, and analyzed. The same thing was done in test 2, but
The difference was that H ₂ O ₂ was added along with NaOH. H ₂ O ₂ in the form of an aqueous solution was added in an amount of 0.21% calculated on the bone-dry pulp. This addition meant that the amount of H ₂ O ₂ per kg of water present was 0.3 g. The test was completed by washing, drying and analyzing the pulp. The results from Test 1 and Test 2 and the test according to the invention of Example 1 are shown in Table 3.

TABLE From the above table it is clear that the pulp produced according to the invention is much better than the pulp according to test 1 and test 2 in terms of Kappa number, extractables and brightness. The difference in extraction is particularly large. In test 2, the same amount of chemicals as in the method of the invention, namely NaOH + H ₂ O ₂ were added.
Nevertheless, the process of the invention gives a pulp that is better not only in terms of resin content, but also in terms of Kappa number and brightness, as mentioned above. These tests show that it is not the added chemicals themselves that account for the good quality of the pulp treated according to the invention. Example 3 Screened cavasulfate pulp was used for the test according to the invention and for the comparative test (O-test). Pulp properties are shown in Table 4. Table 4 Kuppa Number 18.7 Viscosity, dm ³ /Kg 1182 Extractable DCM, % 0.88 Brightness 31.7 Prior to treatment according to the invention, the screened pulp was subjected to delignification bleaching with chlorine and chlorine dioxide. Chlorine and chlorine dioxide are each calculated as active chlorine for bone-dry pulp.
It was added to the pulp simultaneously in amounts corresponding to 3.4% and 0.3%. The temperature was 40°C and the time was 30 minutes. The pulp was then washed. The pulp partially delignified in the manner described above was subjected to the treatment according to the invention using the apparatus shown in FIG. Via a pulp conduit 1 having a temperature of 58°C it is sent to a screw press 2, in which the pulp is
Dehydrated to 27.8%. The forced water was removed through conduit 3. At the outlet of the screw press 2, alkali in the form of NaOH was added to the pulp in an amount of 1.85%, calculated on bone dry pulp. This addition is 7.1g per kg of water present.
It became the alkaline amount of NaOH. The alkali was stored in the form of an aqueous solution in a container 4 and sent to the screw press 2 through conduits 5 and 6. From the screw press 2, the pulp was sent through a conduit 7 to a screw feeder 8. With Screw Feeder 8, the pulp is produced by MoDoMekan AB
It was sent to Screw Defibrator 9, a type sold under the name FROTAPULPER. Immediately before the screw defibrator, hydrogen peroxide H ₂ O ₂ was added to the pulp in an amount of 0.33%, calculated on the bone-dry pulp. The addition was 1.3 g H ₂ O ₂ of peroxide per kg of water present. Hydrogen peroxide in the form of an aqueous solution was stored in container 10 and passed through conduits 11 and 12 to the pulp. In the screw defibrator, the pulp was subjected to a kneading and shearing process corresponding to an energy input of 38 kWh per ton. As a result, the pulp temperature rose to 67°C. After this the pulp passes through a vertical shaft and conduit 13 to column 14
gravity caused it to fall. Pulp and chemicals in tower 14
The reaction with NaOH + H ₂ O ₂ was carried out to completion.
Samples of the pulp were taken after residence times in column 14 of 10, 30 and 120 minutes. Samples were washed, dried and analyzed. The results of the analysis are shown in Table 5. For comparison, partially delignified pulp was subjected to conventional treatment with both chemicals, NaOH and H ₂ O ₂ . Some amount of pulp was sent to a processing vessel, which was kept at 67°C in a water bath. 1.85% NaOH and calculated on bone dry pulp
0.33% _H2O2 was mixed into the pulp by a propeller agitator _. At this time, the pulp density is 12%
It was hot. The addition of these chemicals is 2.5 g of NaOH per kg of water present and 0.5 g of H ₂ O ₂ per kg of water present.
It was equivalent to The pulp and chemicals were allowed to react for 120 minutes, after which the pulp samples were washed, dried, and analyzed. The results of the analysis are shown in Table 5.

[Table] The above analytical results show that even at short residence times after mild mechanical treatment, the process according to the invention gives a lower Kuppa number, higher whiteness and a considerably lower resin content compared to the conventional process. Show that. It is also clear that the increase in residence time in the final stage according to the invention is advantageous in particular for the brightness of the pulp. Example 4 Mainly Eucalyptus saligna and
Partially screened sulfate pulp made from mixed softwood consisting of Eucalyptus grandis was used for the tests according to the invention and for comparative tests (O-tests). The analytical data for the pulp is shown in Table 6. Table 6 Katsupa Number 22.2 Viscosity, dm ³ /Kg 1170 Extractable DCM, % 0.91 Brightness ISO, % 34.9 Partial screening means that knots and large pieces of wood are removed from the pulp, but material normally classified as shive means that they were not separated. This pulp was subjected to the treatment according to the invention using the apparatus shown in FIG. The pulp having a temperature of 55°C is sent through conduit 1 to screw press 2, in which the pulp is
Dehydrated to 31.0%. The forced water was removed through conduit 3. At the outlet of the screw press 2, alkali in the form of NaOH was added to the pulp in an amount of 0.95%, calculated on the bone-dry pulp. This addition is 4.3g per kg of water present.
It became the alkaline amount of NaOH. The alkali was stored in the form of an aqueous solution in a container 4 and sent to the screw press 2 through conduits 5 and 6. From the screw press 2, the pulp was sent through a conduit 7 to a screw feeder 8. With Screw Feeder 8, the pulp is produced by MoDoMekan AB
It was sent to Screw Defibrator 9, a type sold under the name FROTAPULPER. Just before the screw defibrator, it is added to the pulp, calculated as active chlorine for bone dry pulp.
Sodium hypochlorite was added in an amount of 0.55%. The addition was 2.5 g NaClO of hypochlorite per kg of water present. Sodium hypochlorite in the form of an aqueous solution is stored in a container 10 and in a conduit 1
1 and 12 to the pulp. In the screw defibrator, the pulp was subjected to a kneading and shearing process corresponding to an energy input of 26 kWh per ton. As a result, the pulp temperature rose to 63°C. Thereafter, the pulp was allowed to fall by gravity through a vertical shaft and conduit 13 into column 14. The reaction of the pulp with the chemicals HaOH and NaClO in column 14 was carried out to completion. tower 1
After a residence time of 120 minutes in 4 minutes, samples of the pulp were taken, washed, dried, and analyzed. The results of the analysis are shown in Table 7. For comparison, partially screened pulp was subjected to conventional treatment with both chemicals, NaOH and NaClO. An aliquot of pulp was sent to a processing vessel and kept at 63°C in a water bath. 0.95% NaOH calculated on bone dry pulp and 0.55% calculated as active chlorine on bone dry pulp
of NaClO was mixed into the pulp by a propeller agitator. At this time, the pulp concentration was 12%. The addition of these chemicals per kg of water present
1.3g NaOH and 0.8g NaClO per kg water present
corresponds to the amount of The pulp and chemicals were then allowed to react for 120 minutes, after which the pulp samples were washed, dried, and analyzed. The results of the analysis are shown in the seventh
Shown in the table.

[Table] The above analytical data show that the present invention has a lower Kuppa number, higher brightness and significantly higher brightness than pulp treated by conventional methods, even when the oxidizing bleach consists of sodium hypochlorite. shows a low resin content. Two pulps obtained by the described method were tested to detect their impurity content. A sample of the pulp was screened on a Somerville type screen and the amount of material remaining on the screen plate with slot size 0.15 mm was determined. Untreated or partially screened pulp was also tested. The results are shown in Table 8.

[Table] Amount of Yaibu, %
From the above values it is clear that the method according to the invention is also particularly effective for removing particulates from pulp. Example 5 Screened stone-ground pulp made from spruce was used for tests according to the invention and for comparative tests. To remove heavy metals, the pulp was treated with 0.2% (calculated on bone-dry pulp) diethylenediaminepentaacetic acid for 2 hours at a temperature of 65°C. The pulp properties are listed in Table 9. The apparatus shown in FIG. 1 was used in tests according to the invention. The pulp having a temperature of 50°C is sent through conduit 1 to screw press 2, in which the pulp is
Dehydrated to 31%. The forced water was removed through conduit 3. At the outlet of the screw press 2, the mixture of alkali and sodium silicate is
Added to the pulp in an amount of 1.8% NaOH and 4.0% Na ₂ SiO ₃ calculated on bone dry pulp. This addition is 8.1g NaOH per Kg of water present.
A mixed chemical of sodium hydroxide and sodium silicate corresponding to 18 g of Na ₂ SiO ₃ was stored in the form of an aqueous solution in container 4 and sent to screw press 2 through conduits 5 and 6. From the screw press 2, the pulp was sent through a conduit 7 to a screw feeder 8. With Screw Feeder 8, the pulp is from MoDoMekan AB.
It was sent to Screw Defibrator 9, a type sold under the name FROTAPULPER.
Immediately before the screw defibrator, apply 3% hydrogen peroxide to the pulp, calculated on bone dry pulp.
_{H2O2 was} added. The addition was 13.5 H ₂ O ₂ peroxide per kg of water present. Hydrogen peroxide in the form of an aqueous solution is stored in a container 10 and conduit 1
1 and 12 to the pulp. per pulpton in screw defibrator
It was subjected to a kneading and shearing process corresponding to an energy input of 35 kWh. As a result, the temperature of the pulp rose to 58°C. Thereafter, the pulp was allowed to fall by gravity through a vertical shaft and conduit 13 into column 14. Pulp and chemical NaOH in tower 14
The reaction between Na ₂ SiO ₃ and H ₂ O ₂ was carried out to completion.
After a residence time of 120 minutes in column 14, a sample of the pulp was taken. Samples were washed, dried and analyzed. The results of the analysis are shown in Table 9. For comparison, the screened and pretreated pulp was subjected to conventional treatment with three chemicals, NaOH, Na ₂ SiO ₃ and H ₂ O ₂ . Some amount of pulp was sent to a processing vessel, which was kept at 60°C in a water bath. 1.8% calculated for bone dry pulp
NaOH, 4.0% Na ₂ SiO ₃ and 3% H ₂ O ₂ were mixed into the pulp by a propeller agitator. At this time, the pulp concentration was 12%. The addition of these chemicals is 2.5 g of NaOH per kg of water present,
This corresponded to 5.5 g of Na ₂ SiO ₃ and 4.1 g of H ₂ O ₂ . The pulp and chemicals were allowed to react for 120 minutes, after which the pulp samples were washed, dried, and analyzed for brightness and extractables. The results of the analysis
Shown in the table. Besides whiteness and extractables, various pulps were tested to detect their impurity content. A sample of the pulp was passed through a Somerville-type screen (Sommerville, JL, Proc.Tech.Sect.
Papermaker's Assoc. (1932) 13 , 37) and the amount of material remaining on a screen plate with slot size 0.15 mm was measured. The results are shown in Table 9.

TABLE The above data show that the process of the present invention provides pulp with increased brightness and substantially lower resin content compared to conventionally treated pulp. It is also clear that the method of the present invention is very effective in removing particles. Example 6 The procedure of Example 1 was repeated using spruce sulfite pulp made from fresh wood, with the following differences. a Pulp properties

[Table] b Energy input 35 kWh/t Pulp H ₂ O ₂ Charge amount 0.30% vs. absolutely dry pulp c Reaction time of pulp with NaOH and H ₂ O ₂ 3
Minutes (out of range), 10 minutes and 15 minutes results are shown below.

[Table] From these results, the resin content decreased to 0.21% even after 3 minutes of reaction time, 0.15% after 10 minutes, and 0.15% after 150 minutes.
It decreased to 0.14%. Furthermore, it is noteworthy that if H ₂ O ₂ is not added, the whiteness of the pulp will decrease from the original value of 69.0% to about 67%, but by adding H ₂ O ₂ , it will increase to about 73%. be. In the embodiments described above, alkali in the form of sodium hydroxide is always added to the pulp at the outlet of screw press 2 via conduits 5, 6 in FIG. Oxidizing bleach is always present in conduits 11 and 12.
It is added just before the screw defibrator. However, alkaline and oxidizing bleaches can and are advantageously added at multiple locations according to the invention. For example, alkali is in conduit 5
It can be added to the pulp in the screw feeder via. Furthermore, the alkali is in conduit 1
5 to the pulp in the screw defibrator. It is also possible to divide the alkali addition into many, perhaps all, of the above-mentioned addition locations. The oxidizing bleach can be added to the pulp in the defibrator 9 via the main conduit 11. Also, the oxidizing bleach is in conduit 1
1 and 16 to the screw press 2 and via conduits 11, 16 and 17 to the pulp in the screw feeder 8. Corresponding to the addition of alkali, it is possible to divide the oxidizing bleach into many, perhaps all, of the above-mentioned points of addition. If it is necessary to increase the temperature, conduit 1
Steam can be added to the pulp in the screw feeder 8 through 8.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of an apparatus used to carry out the method of the present invention. 2 is screw press, 4 is alkaline container, 8
is the screw feeder, 10 is the bleach container, 1
4 is a tower.

Claims (1)

[Claims] 1. Lignocellulose material is separated into fibers, washed,
The bleached or unbleached pulp obtained by optional screening and optional delignification bleaching is prepared to a pulp concentration of 15 to 35%, preferably 19 to 29%, and an alkali-containing chemical is added, after which the pulp is In a device with screws rotating with respect to each other, it is subjected to a mild mechanical treatment with an energy input of 8 to 100 kWh per pulpton, preferably 10 to 75 kWh per pulpton, after which it is substantially removed in a separate container. A method for reducing resin content in the production of cellulose pulp from lignocellulosic material comprising reacting with added chemicals at the same pulp concentration for 0.1 to 5 hours, the addition of the chemicals being combined with an oxidizing bleach; Kg of water present
A process as described above, characterized in that it consists of 0.5 to 17 g of alkali, calculated as NaOH per liter. 2 to 0.2 per kg of water in which oxidizing bleach is present
22 g, preferably 0.3 to 11 g. 3. The method according to claim 1 or 2, wherein the oxidizing bleach is a peroxidizing bleach. 4. The method according to claim 1 or 2, wherein the oxidizing bleach is hypochlorite. 5. The method according to any one of claims 1 to 4, wherein the alkali is sodium hydroxide.