FI119062B - Process for the manufacture of mechanical pulp - Google Patents

Description

119062

Process for the preparation of mechanical pulp

The present invention relates to a process for the production of mechanical pulp.

5

Fl 61926 and the corresponding DE 2444475 disclose a process wherein the pulp is treated with ozone. It is possible that the pulp pH is adjusted after ozonation.

F 67412 and corresponding CA 1083870 disclose a process in which a mass is fractionated and one fraction, optionally a coarse fraction, is treated with ozone. During ozonation, alkali is introduced into the process.

A problem with the ozonation process is that it produces concentrated organic acids. Organic acids lower the pH of the pulp, which causes problems in the bleaching process, for example when iron-containing substances are precipitated from process water. Organic acids also consume process equipment by causing corrosion.

The above drawbacks can be overcome by the process of the invention. The method comprises the following steps: ···. - feed the raw materials of the mechanical pulp, .v. - milling the raw materials in the first milling step to form a mechanical pulp, • · pH "Y 25 - adjusting the pH of the mechanical pulp to between 9 and 11 in the process step, with a first process delay of at least 0.5 hours, - dividing the mechanical pulp into the first accepted fraction and • · v: the first rejected fraction, 30 - treating the first rejected fraction having a pH between 9 and 11 at the start of the ozonation process, - the first rejected fraction from its fibers in the second refining step **: · in such a way that at least some of it belongs to another accepted fraction, and ϊ ... ϊ - combines the accepted fractions.

·: ··: 35 2 119062

The mechanical pulp is treated so that after the ozonation process the pulp has a constant pH throughout the pulp, which makes it easier to bleach. Compared with prior art mechanical pulp ozonization processes, the new process provides the following benefits: 5 - lower energy consumption to achieve pulp freeness target value, - improved strength properties, - post-ozonization process equipment corrosion inhibition by pH of more than 4, and - improved pulp final.

In the process of the invention, a raw material for mechanical pulp is fed to the process. The raw material may be softwood species such as pine 15 (Pinus sytvestris), southern pine (Pinus genus, various species), spruce (Picea abies), or mixtures of pine and spruce. Deciduous species and mixtures of these and coniferous species are also possible raw materials. The raw material may be in the form of chips. The starting material may also be logs which are milled in a pressure groundwood (PGW) process.

20; * ··. A raw material such as chips that are dewatered to obtain a consistency which. ! ·. in the range of 25-35%, typically 30%, is fed to a refiner, where it is ground in a first refining step. The grinders may be a disk refiner or a cone refiner. The raw material is ground in a refiner at elevated temperature and pressure to form a mechanical pulp. The first grinding step • · · * ”· * can also be done with a hammer mill.

·· ♦

The most suitable raw material is pine because the process according to the invention is sV: most advantageous compared to other processes when the raw material is pine. It is: [*]: 30 commonly known to have low pile defibrillation. However, it can be improved by Tonk with ozone. Ozone-treated pulp contains less ::: fines and sticks than non-ozone-treated pulp. Ozone treatment also has a beneficial effect on the resin removal, which is important in connection with pine raw material.

·! ··: 35 3 119062

The first stage grinding is quite light; the pulp is milled to a free ness of 600-700 ml CSF. The upper limit may be up to 700 ml CSF.

After the first milling step, there are two main options: 1) all 5 mechanical pulps can be fed to an alkali treatment reactor, or 2) the pulp can be divided into a first accepted fraction and a first rejected fraction, and the rejected fraction is led to an alkali processing reactor.

According to the first main alternative, the mechanical pulp is introduced in its entirety into an alkali treatment reactor to achieve a certain pH. The mechanical pulp is treated with an alkali such as sodium hydroxide (NaOH), sodium bicarbonate (Na 2 CO 3), magnesium hydroxide (Mg (OH) 2) or calcium hydroxide (Ca (OH) 2). The process is arranged in an alkali treatment reactor with a process delay, i.e. the pulp remains in the reactor for at least 15 0.5 hours, usually 1-2 hours. The process delay is necessary because the alkali should penetrate from the surface of the pulp fibers to the inner parts of the fibers (or fiber deposits, depending on how coarse the pulp is), i.e. the inner parts of the fibers and / or fiber deposits should be treated. The process delay can be arranged for both the batch process and the continuous process.

20. · * ·. Once the pulp has been treated in an alkali treatment reactor, it is led to a separator, • · ·. such as a sieve or cyclone. The mechanical pulp is divided into the first accepted fraction and the first rejected fraction. The separation step • * * occurs at 0.5-1.5% consistency, typically about 1% "V 25 consistency, and after the separation, the first accepted fraction remains at this * · · *; j; * consistency. The ratio between the accepted fraction and the rejected fraction may usually * ··· * may be about 20/80, but the ratio between the accepted fraction and the rejected fraction may also be 60/40 or 50/50, so the accepted fraction may be 20 -: v 60% of the total mass or up to 15 -65% of the total mass.

t · · * φ ·

Initially, the first rejected fraction is dewatered, so that the consistency of the first '*: ** rejected fraction is preferably greater than 30%. The consistency is more preferably over s ..,! 35%. The excess liquid is recycled to the process. The first *: **: 35 rejected fraction is conducted at the above consistency to an ozone reactor where the first rejected fraction is torn and ozonated. Depending on the requirements for energy savings and the quality of the 4119062 pulp, the ozonation process is arranged so that the amount of ozone is 0.5-10% and preferably 1-4% by weight of the pulp. The process temperature is 20 ... 90 ° C. Strong organic acids are formed in the ozonation process, but the alkali used to treat the first rejected fraction neutralizes these strong organic acids. Strong organic acids and alkali form a buffer solution that can be maintained at a certain level for a long period of time, although organic acids are continuously formed in the ozonation process. At the end of the ozonation process, the pH of the rejected fraction is between 5 and 7, which is an advantageous range for the subsequent process steps.

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After ozonation, the first rejected fraction is ground in a main refining line, which may comprise successive refiners. It is possible that the first rejected fraction is divided into a second accepted fraction and a second rejected fraction. The second rejected fraction may be led to further milling, i.e. the third milling step, but it is also possible that it is only removed from the process. If there is a third refining step, it is performed in the same way as the previous refining steps.

After the above process steps, the first accepted fraction and the accepted portion of the first 20 rejected fractions are combined. Reject the first. * · *. The accepted portion of a verse means any accepted verse that is. ! ·. obtained after dividing the mass into the first accepted fraction • ♦ «, v. and the first rejected fraction.

It is possible that the first approved fraction is treated with ozone and the ozone-treated pulps are combined. It is also possible that alkali is added to the first approved fraction after this has been treated with ozone. The alkali may be the one added before the ozonation. In addition, it is possible that the approved fraction, which is not ozonized, is treated with alkali 30 before being combined with the approved portion of the first rejected fraction.

· · "Il The resulting freeness can have a freeness of 90-150 ml CSF, but it is also possible that the lower limit is 30 or 40 ml CSF. It is clear that the freeness mentioned above s ***: value depends on the desired paper quality.

·: ··: 35 5 119062

According to the second main alternative, after the first milling step, the pulp is divided in a separator, such as a screen or cyclone, into the first accepted fraction and the first rejected fraction. The separator has a consistency of 1-2%. The ratio between the accepted fraction and the rejected fraction can generally be about 20/80. However, the ratio between the accepted fraction and the rejected fraction may also be 60/40 or 50/50. Thus, the accepted fraction may be 20-60% of the total mass, or even 15-65% of the total mass.

The first rejected fraction is treated with an alkali such as sodium hydroxide (NaOH), sodium bicarbonate (Na 2 CO 3), magnesium hydroxide (Mg (OH) 2) or calcium hydroxide (Ca (OH) 2) in an alkali treatment reactor. The pH of the first rejected fraction is raised to 9-11, which depends on the amount of ozone used and the raw material treated. Thereafter, the first 15 rejected fractions are dewatered to obtain a consistency, preferably greater than 30%. More preferably, the consistency is greater than 35%. The excess liquid is recycled to the process. At the above consistency, the first rejected fraction is fed to an ozone reactor, where the first rejected fraction is torn and ozonated. Depending on the requirements of energy saving and pulp quality, the ozonation process is arranged so that the amount of ozone is 0.5-10% and preferably 1-4% by weight of the pulp. Process heat; the temperature is 20 ... 90 ° C. Strong organic acids are formed in the ozonation process, but the alkali used to treat the first rejected fraction neutralizes these strong organic acids. Strong organic acids and alkali • · · "V 25 form a buffer solution that can be maintained at a certain level for a prolonged period of time, although organic acids * ··· * and jatkuvasti are continuously formed during the ozonation process. an advantageous area for the following process steps.

After ozonation, the first rejected fraction is fed to the refiner to perform the second refining step. When the first rejected fraction is treated with ozone, its properties have changed so that the • • T stage of the second refining process consumes much less energy than pulps not treated with ozone. The first rejected fraction is passed from the refiner to a screener which separates the first rejected fraction into a second accepted fraction and a second rejected fraction. The freeness of the accepted fractions, i.e. the mass of the first accepted fraction and the second accepted fraction, may be 90-150 ml CSF, but the lower limit may also be 30-40 ml CSF. It is clear that the above-mentioned freeness value depends on the desired paper quality.

The second rejected fraction may be derived from further milling, i.e. the third milling step, but it is also possible that it is merely removed from the process. If there is a third refining step, it is performed in the same way as the previous refining steps.

The first accepted fraction may be removed from the process and used for other purposes, but it is also possible that the first accepted fraction and the second accepted fraction may be combined so that they can be conducted as one fraction to the next process step, which is usually a bleaching step. The pH of the pulp from the first milling step is in the range of 15 to 7, and the first accepted pulp has approximately the same pH, so no further steps are required to adjust the pH.

Adjusting the pH to 9-11 before grinding facilitates the bleaching step as peroxide consumption is reduced. Harmful wood extractants dissolve in 20 water to which alkali is added.

* ·· • «• · ···. . ·. The mechanical pulp obtained by the present invention (the first and above mentioned * and the second main alternatives mentioned above) is used in the paper product manufacturing process. Pape- · *. *. the paper product may be mechanical pulp, such as mechanical • · · "V 25 pulp, or it may be paperboard.

The invention will now be described, by way of example and with reference to the drawings, in which: Figure 1 schematically illustrates the first process, Figure 9 schematically the second process, · · · · · ··· Figure 3 schematically shows the third and fourth processes, ·: · *: 35 7 119062 Figure 4 shows the tensile index as a function of specific energy consumption (SEC), and Figure 5 shows the tear index as a function of tensile index.

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Example 0.

For the treatment of mechanical pulp made of pine, non-alkali treatment prior to ozonation was used.

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Points 1 and 2 correspond to the results obtained with standard hot rolling (TMP) using pine as the raw material.

The dot 5 in Figures 5 and 6 corresponds to the results obtained from the process of mixing ozone-15 witch abandoned pine fractions with non-ozone-approved pine fractions. No alkali has been added.

Point 7 in Figures 5 and 6 corresponds to the results obtained from the process of mixing an ozone depleted pine fraction with an ozonated accepted pine 20 fraction. No alkali has been added.

As can be seen in Figures 5 and 6, ozonation of the rejected pine fraction yielded ± 20% energy savings and better strength properties than the conventional pine process.

i · · _ _ * ·· .1 25: · * Example 1.

8 119062 is the most advantageous compared to other processes where the raw material is pine. The first stage grinding is quite light; pulp is defibrated to a free ness of 600-700 ml CSF. It is possible that the freeness value is up to 700 ml CSF. The pulp is treated with an alkali, such as sodium hydroxide, in an alkali-5 treatment reactor 3. The pH of the first rejected fraction is raised to 9-11. The alkali treatment reactor 3 has a delay so the pulp remains inside the alkali treatment reactor for at least 0.5 hours, usually 1-2 hours. The pulp is also diluted in an alkali treatment reactor, so that its consistency is 0.5-1.5%.

The mass is divided by a screen 4, such as a screen, into the first accepted fraction A1 and the first rejected fraction R1. Generally, the ratio of accepted fraction to rejected fraction is about 20/80, but other ratios described in the general description are also suitable.

Thereafter, the first rejected fraction R1 is introduced into a thickener 5, such as a screw press, which removes fluid from the pulp to achieve a consistency greater than 35%. The excess liquid 9 is recycled to the process. The first rejected fraction R1 is conducted at the above consistency to an ozone reactor 6 where the first rejected fraction R1 is ozonated. In the ozonation process, strong organic acids are formed, but these strong • · ': organic acids are neutralized by the alkali used to treat the first rejected fraction. Strong organic acids and alkali form a buffer solution whose pH can be maintained at a certain level for a long period of time, although organic acids are continuously formed in the ozonation process. At the end of the ozonization process, the pH of the rejected fraction is between 5 and 7, which is an advantageous range for the following process steps.

«· • * * · ·

After ozonation, the first rejected fraction R1 is fed to a refiner 7.

* · \ V When the first rejected fraction R1 is treated with ozone, its properties have changed so that much less energy is consumed in the refining step than in non-ozone treated pulps. The first rejected fraction R1 can-] · * ·. It is also possible that the * m V first rejected fraction is passed to a screener (not shown) which sorts the first rejected fraction to the second accepted fraction and the second *: **: 35 rejected fraction. The second rejected fraction may be led to further milling, but it is also possible that it is merely removed from the process.

9 119062

The first accepted fraction and the accepted portion of the first rejected fraction can be combined after the first rejected fraction has been treated as above, so that they can be conducted as one fraction to the next process step, which is usually a bleaching step. The resulting pulp has a pH in the range of 5-7.

The point 4 in Figures 4 and 5 corresponds to the result obtained by the above process.

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Example 2.

The second process will now be described with reference to Figure 2.

The raw material of the mechanical pulp is first dehydrated, for example, in a thickener 1, such as a screw press, and then the raw material is fed to a refiner 2 where the raw material, such as chips, is pulverized at elevated temperature and pressure to form mechanical pulp. The consistency of the pulp is about 30%. The most suitable raw material 20 is pine because the process according to the invention is most advantageous compared to other processes when the raw material is pine. Phase One: · *: The hat is quite light; the pulp is milled to a freeness of 600- ··· 700 ml CSF. The pulp is treated with an alkali such as sodium hydroxide, alkali:. in the treatment reactor 3. The pH of the first rejected fraction is raised to 9 t * ·) * V 25 11. There is a delay in the alkali treatment reactor 3 so that the pulp remains inside the alkali treatment reactor for at least 0.5 hours, usually 1-2 hours. At the same time, the mass ** ·· * dilutes to a consistency between 0.5 and 1.5%.

• *: .v The mass is sorted in a screen 4, such as a screen, into the first accepted • e · 30 fraction A1 and the first rejected fraction R1. The ratio of accepted versus rejected verses is usually about 20/80, but other ratios are '··. suitable.

Thereafter, the first rejected fraction R1 is fed to a thickener 5, such as a 35 jig press, which removes fluid from the pulp to achieve a consistency greater than 35%. The excess liquid 9 is recycled to the process. The first rejected fraction R1 is conducted at the above consistency to an ozone reactor 6 where the first rejected fraction R1 is ozonated. The amount of ozone is 0.5-10% and preferably 1-4% by weight of the pulp. During ozonation the temperature is 20 ... 90 ° C.

5

Strong organic acids are formed in the ozonation process, but the alkali used to treat the first rejected fraction neutralizes these strong organic acids. The strong organic acids and alkali form a buffer solution that can be maintained at a certain level for a long time, although organic acids are continuously formed in the ozonation process. At the end of the ozonation process, the pH of the rejected fraction is between 5 and 7, which is an advantageous range for the subsequent process steps.

After ozonation, the first rejected fraction R1 is passed to a screen 7. When the first rejected fraction R1 has been treated with ozone, its properties have changed so that much less energy is consumed in the second refining stage than the non-ozone treated pulps. The first rejected fraction R1 can be passed from the refiner 7 to the second refiner 8. It is also possible that the first rejected fraction is passed to a sorter (not shown) which sorts the first rejected fraction to the second accepted fraction and to the *** rejected fraction. The second rejected fraction may be derived from the continuous fiber, but it is also possible that it is merely removed from the process.

·· «• · · • · · · 1.!. The first approved fraction A1 is introduced into the ozone reactor 11 at a consistency, ♦ 1 · "V 25 of between 0.5% and 1.5%. The first accepted fraction A1 is ozonated in the ozone reactor 11. The ozone can be injected into the first approved fraction 1 * ··· 1.

The first accepted fraction A1 and the ignited portion of the first rejected fraction R1 can be combined after the first fractions have been treated in the above manner, so that they can be conducted as a single pulp to a subsequent process step, which is usually a bleaching step. The resulting pulp **: 1 'has a pH of 5-7.

e ·· v t • · · 1 «35 Point 6 in Figures 4 and 5 corresponds to the result obtained by the process option described above.

"119062

As can be seen in Figures 4 and 5, energy savings of ± 30% and better strength properties were achieved than the conventional pine process when the rejected pine fraction was treated with alkali and ozone (point 4 and point 6).

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Example 3.

The third process will now be described with reference to Figure 3.

The third process is similar to Figure 2 except that the first approved fraction is treated with alkali after it has been ozonated in the mixing reactor 13. The amount of alkali was 0.5 wt% of the total dry first approved fraction (e.g. 0.5 wt%) 100% NaOH). A process delay is provided in the mixing reactor 13. The mass remains in the reactor 13 for at least 0.5 hours.

The point 8 in Figures 4 and 5 corresponds to the result obtained with the process option described above.

Example 4.

The following describes the fourth process with reference to Figure 3.

··· • · t · # • · ·

The fourth process is similar to Figure 2 except that the first approved fraction of V · 25 is treated with alkali after it has been ozonated * in the mixing reactor 13. The amount of alkali was 2 wt% of the total dry amount of the first approved • 9 * ·· * fraction. (e.g., 2% by weight of 100% NaOH).

A process delay is provided in the mixing reactor 13. The mass remains in the reactor for 13 years for at least 0.5 hours.

··· 30

Point 9 in Figures 4 and 5 corresponds to the result obtained by the process "**" option described above.

• ·

As can be seen in Figures 4 and 5, energy savings of ± 30% and better strength properties were achieved than the conventional pine process when 9121-19062 rejected pine fraction was treated with alkali, rejected pine fraction was ozonated and alkali was added to the accepted fraction (point 8 and point 9).

It will be apparent to one skilled in the art that the processes described in the Examples above may be combined in various ways. It will also be apparent to one skilled in the art what consistency is required to complete each process step. The order of the first process delay and the sorting step may be reversed; in that case, it will be apparent to one skilled in the art that the consistency must be adjusted and the first accepted fraction and the first rejected fraction treated separately with alkali if such treatment is required for both fractions.

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Claims (8)

13 119062 A process for producing a mechanical pulp, comprising: - introducing the raw materials of the mechanical pulp, 5. milling the raw materials in a first milling step to form a mechanical pulp, - adjusting the pH of the mechanical pulp to 9-11 in a process step having a first process delay of at least 0, 5 hours, 10. sort the mechanical pulp into the first accepted fraction (A1) and the first rejected fraction (R1), - treat the first rejected fraction (R1) with a pH between 9 and 11 at the start of the ozonation process, - sort the ozonated first rejected fraction (R1) ) in the second milling step 15, at least part of which is in the second accepted fraction, and - combining the approved fractions. Process according to Claim 1, characterized in that the first rejected fraction (R1) is ozonated at a consistency of more than 30%. e ·· • · * · ···. . ·. Method according to claim 1 or 2, characterized in that in the treatment of the first rejected fraction (R1), i - sorting the ozonized and ground first rejected fraction (R1) into a second; * V 25 accepted fraction and a second rejected fraction. • · · ··· • • e A method according to any one of the preceding claims, characterized in that, in the treatment of the first accepted fraction (A1), the first accepted fraction (A1) is ozonated. * ·· ϊ ** 30 A process according to claim 4, characterized in that the first accepted fraction (A1) is ozonated at a consistency of 0.5-1.5%. The method according to any one of the preceding claims, characterized in that in processing the first accepted fraction (A1), an additional alkali is added to the ozonated first accepted fraction (A1) in a process step provided with a second process delay of at least 0, 5 hours. Method according to one of the preceding claims, characterized in that the approved fractions are bleached. Use of a mechanical pulp made according to any one of the preceding claims in a paper product manufacturing process. 10 aaa • • • «« te * • · aaa e · aaa aaa • a • a • • i aaa aaa a • • aaaam ·· «··· • * aa aaa • a aaa aaa aa aaa aaa aa • aa a aaaa aaa • aaa aaa a aaa aaaa aaa aaa 119062 15