JP7473221B2 - Chemical pulp manufacturing method - Google Patents

Description

This disclosure relates to a chemical pulp manufacturing method, a cooking method, and a pulp cooking aid.

Chemical pulp, that is, methods for producing pulp by chemically treating lignocellulosic materials, include alkaline cooking and sulfite cooking. The alkaline cooking methods referred to in this disclosure include a wide variety of methods, such as kraft cooking, soda cooking, sulfite cooking, and organosolv cooking. Furthermore, the sulfite cooking method (sulfite method) referred to in this disclosure is a general term for various sulfite methods, including the alkaline sulfite method, neutral sulfite method, acidic sulfite method, and bisulfite method.

Anthraquinone has been widely used as a cooking aid. However, in recent years, the carcinogenicity of anthraquinone has come to light, and in 2013 the German Federal Institute for Risk Assessment (BfR) announced that it would remove anthraquinone from the list of substances approved for use in food packaging paper, and is moving toward discouraging its use. For this reason, new cooking aids to replace anthraquinone are being developed.

Patent Document 1 discloses alkaline cooking of lignocellulosic materials using a cooking liquor to which a nonionic surfactant and/or an anionic surfactant has been added. Patent Document 2 discloses a cooking aid containing a _nonionic surfactant represented by ^R1 -O-[( _C2H4O ) _m /( ^A1O ) _n ]-H, and alkaline cooking of _{lignocellulosic} materials using a cooking liquor to which the cooking aid has been added. Patent Document 3 discloses a cooking aid containing _a compound represented by R[( _C2H4O ) _n ( _C3H6 ) _mO ] _xH .

JP 2019-173241 A JP 2001-064888 A U.S. Pat. No. 3,909,345

However, cooking using conventional surfactants has problems such as lower yields and higher kappa numbers compared to cooking using anthraquinone as a cooking aid.
Therefore, in one or more embodiments, the present disclosure provides a chemical pulp production method and cooking method that can produce chemical pulp with a low kappa number while suppressing a decrease in yield compared to when a conventional surfactant-based cooking aid is used, and a cooking aid used therein.

The present disclosure provides, in one aspect, a method for producing chemical pulp comprising alkaline cooking or sulfite cooking of a lignocellulosic material with a cooking liquor comprising a Pluronic-type nonionic surfactant that is a polyoxyethylene polyoxypropylene block polymer,
the ratio (EO:PO) of oxyethylene groups (EO) to oxypropylene groups (PO) in the nonionic surfactant is 55:45 to 85:15 (weight ratio);
The weight average molecular weight of the oxypropylene group in the nonionic surfactant is 200 to 900.

In another aspect, the present disclosure provides a method for cooking lignocellulosic material, comprising alkaline cooking or sulfite cooking the lignocellulosic material with a cooking liquor comprising a Pluronic-type nonionic surfactant that is a polyoxyethylene polyoxypropylene block polymer, the method comprising:
the ratio (EO:PO) of oxyethylene groups (EO) to oxypropylene groups (PO) in the nonionic surfactant is 55:45 to 85:15 (weight ratio);
The weight average molecular weight of the oxypropylene group in the nonionic surfactant is 200 to 900.

In another aspect, the present disclosure provides a cooking aid for lignocellulosic material, comprising a Pluronic-type nonionic surfactant that is a polyoxyethylene polyoxypropylene block polymer, comprising:
the ratio (EO:PO) of oxyethylene groups (EO) to oxypropylene groups (PO) in the nonionic surfactant is 55:45 to 85:15 (weight ratio);
The present invention relates to a cooking aid in which the weight average molecular weight of the oxypropylene group in the nonionic surfactant is 200 to 900.

In one or more embodiments, the present disclosure can provide a chemical pulp production method and cooking method that can produce chemical pulp with a low kappa number while suppressing a decrease in yield compared to when a conventional surfactant-based cooking aid is used, as well as a cooking aid used therein.

FIG. 1 is a block diagram showing an example of the flow of a chemical pulp production system. FIG. 2 is a graph showing the results of the Examples and Comparative Examples (ΔKN: Kappa number, ΔY _screened : yield).

The present disclosure is based on the finding that the kappa number of the resulting pulp can be reduced by cooking in the presence of a Pluronic-type nonionic surfactant having an EO:PO (weight ratio) of 55:45 to 85:15 and a weight average molecular weight of PO of 200 to 900 (hereinafter also simply referred to as "Pluronic-type nonionic surfactant").
The present disclosure is based on the discovery that by cooking in the presence of the above-mentioned Pluronic-type nonionic surfactant, it is possible to achieve a reduction in kappa number while suppressing the decrease in pulp yield compared to the case where a conventional surfactant-based cooking aid is used.
The present disclosure is based on the discovery that by carrying out cooking in the presence of the above-mentioned Pluronic-type nonionic surfactant, it is possible to achieve both a decrease in the kappa number and a suppression of a decrease in the pulp yield while reducing the amount of alkali used in the cooking liquor.

The details of the mechanism by which the above-mentioned effects are achieved by performing cooking in the presence of a Pluronic-type nonionic surfactant in which the EO:PO (weight ratio) is 55:45 to 85:15 and the PO has a weight average molecular weight of 200 to 900 are not clear, but are presumed to be as follows.
While it is known that surfactants improve the permeability of white liquor (such as alkaline solutions and sulfite solutions in the cooking liquor) into lignocellulosic materials, they are also known to inhibit the penetration of white liquor into the intercellular spaces of lignocellulosic materials. In contrast, the surfactant used in the present disclosure has a higher EO:PO (weight ratio) of 55:45 to 85:15 than PO, so that it can maintain the effect of improving the permeability of white liquor into lignocellulosic materials even under heating conditions during cooking. In addition, since the weight average molecular weight of PO is 200 to 900, it is possible to suppress the adverse effects that the surfactant may have on the penetration of white liquor into the intercellular spaces. Furthermore, since it is a Pluronic-type nonionic surfactant, it is possible to suppress foaming (foaming) that may occur during cooking. As a result of these, it is possible to reduce the kappa number of the obtained pulp, and furthermore, it is thought that it is possible to suppress the decrease in pulp yield compared to the case where a conventional surfactant-based cooking aid is used.
However, the present disclosure need not be construed as being limited to these mechanisms.

In one or more embodiments of the present disclosure, the weight average molecular weight of the Pluronic nonionic surfactant can be measured using gel permeation chromatography (GPC). The measurement conditions are, for example, as follows.
<Measurement conditions>
Instrument: 1260 Infinity II LC
Detector: ELSD
Column: PLgel MIXED
Measurement (column) temperature: 40°C
Eluent: THF
Flow rate: 1.0mL/min
Sample concentration: 1%
Sample injection volume: 10 μL
Conversion standard: Polyethylene glycol

In this disclosure, the ratio (weight ratio) of EO and PO in a Pluronic nonionic surfactant can be determined, for example, by NMR (nuclear magnetic resonance) or FT-IR (Fourier transform infrared spectroscopy).

In this disclosure, the weight average molecular weight of PO in a Pluronic nonionic surfactant can be determined, for example, from the number of moles added obtained using NMR or FT-IR.

In this disclosure, "pulp yield (screened yield)" refers to the percentage of the dry weight of pulp (screened pulp) after removing undigested fibers such as knot residue from the unbleached pulp after cooking, relative to the bone dry weight of the entire raw material (lignocellulosic material) used in cooking.
In this disclosure, "bone dry weight" refers to the weight after drying at 105°C for 1 day.
In this disclosure, the term "kappa number" refers to the kappa number obtained by testing the above-mentioned selected pulp in accordance with JIS P 8211 (pulp kappa number test method).

In this disclosure, "chemical pulp" refers to pulp obtained by chemically treating lignocellulosic material to delignify it. In one or more embodiments, examples of chemical pulp include sulfite pulp, dissolving sulfite pulp, alkaline pulp, kraft pulp, and dissolving kraft pulp.

In the present disclosure, the "lignocellulosic material" may be various types of wood such as wood chips, or may be non-wood such as straw. In one or more embodiments, examples of wood include coniferous (N wood) chips and hardwood (L wood) chips. In one or more embodiments, examples of coniferous trees include larch, red pine, and cedar. In one or more embodiments, examples of hardwood trees include eucalyptus and acacia. In one or more embodiments, the lignocellulosic material may be a single type of lignocellulosic material, or may be a mixture of two or more types of lignocellulosic materials. The lignocellulosic material in the present disclosure may include not only the above-mentioned wood chips, but also pulp slurry (e.g., unbleached or unbleached pulp, etc.) discharged from the digester (digestion process).

In this disclosure, "cooking" refers to treating wood or non-wood lignocellulosic materials at high temperature and high pressure using chemicals to dissolve or remove non-cellulose materials such as lignin from the lignocellulosic materials and separate cellulose and other cellulose materials. In this disclosure, cooking includes alkaline cooking and sulfite cooking. In one or more embodiments, cooking can be performed by heating the lignocellulosic material and cooking liquid (alkaline solution) in a kettle. In one or more embodiments, high-temperature treatment in this disclosure includes heating to 80°C or higher. In one or more embodiments, cooking in this disclosure includes heating the cooking liquid to a temperature of 80°C to 200°C. In one or more embodiments, high-pressure treatment in this disclosure includes pressurizing to 0.2 MPa or higher, preferably 0.3 MPa or higher or 1.0 MPa or higher. In one or more embodiments, high-pressure treatment in this disclosure includes pressurizing to 3.0 MPa or lower, preferably 2.0 MPa or lower.

[Method of producing chemical pulp]
In one aspect, the present disclosure relates to a method for producing chemical pulp, comprising subjecting a lignocellulosic material to alkaline cooking or sulfite cooking using a cooking liquor containing a polyoxyethylene polyoxypropylene block polymer (Pluronic-type nonionic surfactant) having an EO:PO ratio (weight ratio) of 55:45 to 85:15, and the molecular weight of the PO being 200 to 900. According to the method for producing chemical pulp of the present disclosure, in one or a plurality of embodiments, it is possible to produce a chemical pulp having a low kappa number while suppressing a decrease in yield.

In the present disclosure, the EO:PO ratio (weight ratio) of the Pluronic nonionic surfactant is 55:45 to 85:15, and preferably 60:40 to 80:20 in terms of further reducing the kappa number and/or further suppressing the decrease in yield.

In the present disclosure, the weight average molecular weight of the PO of the Pluronic nonionic surfactant is 200 to 900. From the viewpoint of further reducing the kappa number and/or further suppressing a decrease in yield, the weight average molecular weight of the PO of the Pluronic nonionic surfactant is preferably 300 or more, 350 or more, 400 or more, 450 or more, or 500 or more. From the same viewpoint, it is preferably 850 or less, 800 or less, 750 or less, or 700 or less.

In the present disclosure, the weight average molecular weight of EO of the Pluronic nonionic surfactant is, in one or more embodiments, 500 to 2550. In one or more embodiments, the weight average molecular weight of EO of the Pluronic nonionic surfactant is 600 or more, 700 or more, 800 or more, 900 or more, or 1000 or more. In one or more embodiments, the weight average molecular weight of EO of the Pluronic nonionic surfactant is 2500 or less, 2400 or less, 2200 or less, 2100 or less, 1900 or less, 1700 or less, 1500 or less, 1300 or less, or 1100 or less.

In the present disclosure, the weight average molecular weight of the Pluronic nonionic surfactant is, in one or more embodiments, 500 to 3000. From the viewpoint of further reducing the kappa number and/or further suppressing a decrease in yield, it is preferably 600 or more, 700 or more, 800 or more, 900 or more, 1000 or more, 1100 or more, 1200 or more, 1250 or more, 1300 or more, 1500 or more, or 1700 or more. From the same viewpoint, it is preferably 2900 or less, 2750 or less, 2550 or less, 2300 or less, 2000 or less, or 1800 or less.

The cloud point of the Pluronic nonionic surfactant is preferably greater than 90°C, such as 90.4°C or higher, 94°C or higher, 95°C or higher, or 99°C or higher, in order to further reduce the kappa number and/or further suppress a decrease in yield. The cloud point in this disclosure refers to the cloud point when the surfactant is made into a 1% by mass aqueous solution.

In one or more embodiments, the Pluronic nonionic surfactant in the present disclosure may be a nonionic surfactant that is a triblock copolymer of an oxyethylene group and an oxypropylene group. In one or more embodiments, the Pluronic nonionic surfactant may be a polyoxyethylene polyoxypropylene condensation type, a polyoxyethylene polyoxypropylene block polymer reverse type, an ethynediamine polyoxyethylene polyoxypropylene block polymer type, and a reverse type of ethylenediamine polyoxyethylene polyoxypropylene block polymer.

In one or more embodiments, the polyoxyethylene-polyoxypropylene condensed Pluronic nonionic surfactant is represented by HO(C ₂ H ₄ O) _x1 -(C ₃ H ₆ O) _y1 -(C ₂ H ₄ O) _z1 H. x1 and z1 represent the average number of moles of EO added, each of which is independently 1 to 57, and x1 + z1 is 7 to 58, preferably 11 to 58, and more preferably 17 to 46. y1 represents the average number of moles of PO added, and is 4 to 15, preferably 8 to 15, and more preferably 8 to 13.

In one or more embodiments, the polyoxyethylene polyoxypropylene block polymer reverse type Pluronic nonionic surfactant is represented by HO(C ₃ H ₆ O) _x2 -(C ₂ H ₄ O) _y2 -(C ₃ H ₆ O) _z2 H. x2 and z2 represent the average number of moles of PO added, each independently being 1 to 14, and x2 + z2 being 4 to 15, preferably 8 to 15. y2 represents the average number of moles of EO added, and is 7 to 58, preferably 11 to 58.

The Pluronic nonionic surfactants used in this disclosure can be produced by known methods.

The cooking liquor contains a Pluronic-type nonionic surfactant. In one or more embodiments, the content of the Pluronic-type nonionic surfactant in the cooking liquor is 0.01% to 1% by weight based on the bone dry weight of the lignocellulosic material. In one or more embodiments, the content of the Pluronic-type ionic surfactant is 0.015% by weight or more. In one or more embodiments, the content of the Pluronic-type nonionic surfactant is 0.05% by weight or less or less than 0.05% by weight.
In one or more embodiments, the method for producing chemical pulp of the present disclosure may include adding a Pluronic nonionic surfactant to the cooking liquor so that the content of the Pluronic nonionic surfactant in the cooking liquor is in the above-mentioned range.

In one or more embodiments, the cooking liquor may be a cooking liquor used in alkaline cooking or sulfite cooking. In one or more embodiments, the alkaline cooking method may be a kraft cooking method, a soda cooking method, a sulfite cooking method, or an organosolv cooking method. In one or more embodiments, the sulfite cooking method may be an alkaline sulfite method, a neutral sulfite method, an acidic sulfite method, or a bisulfite method.

In one or more embodiments, the cooking liquor used in the alkaline cooking may be an alkaline solution (alkaline cooking liquor) used in a general cooking process. In one or more embodiments, the alkaline solution contains sodium sulfide (Na ₂ S) and sodium hydroxide (NaOH), and preferably contains sodium sulfide and sodium hydroxide as main components. In one or more embodiments, the sulfidity of the lignocellulosic material per bone dry weight in the alkaline solution is 10% by mass to 35% by mass or 15% by mass to 30% by mass. The sulfidity is expressed as (Na ₂ S)/(NaOH+Na ₂ S)×100. In one or more embodiments, the amount of alkali added per bone dry weight of the lignocellulosic material (active alkali addition rate (AA)) is 5% by mass to 35% by mass or 12% by mass to 24% by mass. The active alkali is expressed by converting the NaOH concentration + Na ₂ S concentration into Na ₂ O, and the active alkali and the sulfidity can be calculated from the following formula.
Active alkali = [amount of NaOH x 61.979 / (2 x 39.997)] + [amount of _Na2S x 61.979 / 78.0452]
Sulfidity=[ _Na2S amount×61.979/78.0452]÷active alkali 61.979: molecular weight of _Na2O 39.997: molecular weight of NaOH 78.0452: molecular weight of _Na2S It is known that the more active alkali added to the cooking liquor, the lower the kappa number can be. In one or more embodiments, the method for producing chemical pulp of the present disclosure involves cooking with a cooking liquor containing a Pluronic nonionic surfactant, so that a reduction in kappa number can be achieved even with a lower alkali addition amount than when cooking with a cooking liquor without a Pluronic nonionic surfactant.

In one or more embodiments, the cooking liquor used in sulfite cooking may be a sulfite solution or a hydrogen sulfite solution (bisulfite solution).

In one or more embodiments, the liquor ratio between the lignocellulosic material and the cooking liquor (the amount of cooking liquor per 1 kg (bone dry weight) of the lignocellulosic material) is 1.0 L/kg to 5.0 L/kg, preferably 0.5 L/kg to 4.5 L/kg or 2.0 L/kg to 4.0 L/kg.

In one or more embodiments, the heating temperature during cooking is 80°C to 200°C, and preferably 140°C to 180°C. In one or more embodiments, the manufacturing method of the present disclosure includes a cooking step that includes heating the lignocellulosic material at 80°C to 200°C in a cooking liquor containing the above-mentioned Pluronic-type nonionic surfactant.

In one or more embodiments, the heating time during cooking is 30 minutes to 400 minutes, preferably 50 minutes to 300 minutes.

The location of addition of the Pluronic nonionic surfactant is not particularly limited as long as it is added so that the lignocellulosic material is cooked in a cooking liquor containing the Pluronic nonionic surfactant. In one or more embodiments, the location of addition of the Pluronic nonionic surfactant may be at least one location from the raw material chip supply step prior to the cooking step to the cooking step in which the lignocellulosic material is subjected to alkaline cooking or sulfite cooking. In one or more embodiments, the Pluronic nonionic surfactant may be added to the digester in which cooking is performed, or, from the viewpoint of further reducing the kappa number and/or further suppressing the yield reduction, it is preferable to add it to any of the raw material chip supply steps in which raw material chips are supplied to the digester. In one or more embodiments, the location of addition in the raw material chip supply step may be a chip bin (13 in FIG. 1), a steaming vessel (14 in FIG. 1), a metal trap, a chip chute, a high-pressure feeder, and the like. Thus, the manufacturing method of the present disclosure may include mixing the Pluronic nonionic surfactant with the raw material chips. In addition, the Pluronic nonionic surfactant may be added to the injection circulation line of the cooking liquor (white liquor and black liquor), or may be added to the oxygen cooking device in the delignification process after cooking in the digester. In one or more embodiments, the Pluronic nonionic surfactant may be added all at once or in portions.

An example of the flow of a method for producing chemical pulp is shown in Figure 1. The flow of Figure 1 includes a raw material chip supply process of lignocellulosic material, a cooking process, and an oxygen delignification process.
(Raw material chip supply process)
Chips 11 of lignocellulosic material chipped in a chipper (not shown) are stored in a chip silo 12. The chips stored in the chip silo 12 are selected by a chip screen (not shown) and sent to a chip bin 13, and then the gas phase inside the chips is replaced with steam in a steaming vessel 14.
(Digestion process)
The chips, the permeability of which has been increased in the steaming vessel 14, are passed through the impregnation tower 15, where the permeation of the cooking liquor into the chips is promoted. Then, in the digester 16, the wood chips, which are the pulp material, are mixed with a cooking liquor containing at least a Pluronic-type nonionic surfactant and sodium hydroxide, and the mixture is steamed under pressure to discharge a pulp slurry containing a mixture of black liquor in which non-fibrous components have been dissolved and pulp. In some cases, the impregnation tower 15 may be used as a prehydrolysis vessel (PHV) tower for prehydrolysis using an acid.
(Oxygen delignification process)
The pulp slurry discharged from the digester 16 is washed in a black liquor washing tower 17, then passes through a screen 18, a decker 19, and an unbleached high consistency storage tower 20, and is then introduced into an oxygen digester 21. In the oxygen digester 21, further delignification is performed, and the pulp slurry is then transferred to a bleaching process (not shown).

The manufacturing method of the present disclosure may include pretreating the lignocellulosic material prior to the above-mentioned cooking. In one or more embodiments, the pretreatment may include hydrothermal treatment (prehydrolysis treatment) and the like. In one or more embodiments, the hydrothermal treatment may be performed by treating the chip-like lignocellulosic material with hot water or steam.

[Digestion method]
In one aspect, the present disclosure relates to a cooking method that includes alkaline cooking or sulfite cooking of a lignocellulosic material using a cooking liquor containing a Pluronic-type nonionic surfactant having an EO:PO ratio (weight ratio) of 55:45 to 85:15, and a PO weight average molecular weight of 200 to 900. According to the cooking method of the present disclosure, in one or more embodiments, pulp with a low kappa number can be produced while suppressing a decrease in yield. The Pluronic-type nonionic surfactant, its content, cooking conditions, etc. in the cooking method of the present disclosure are the same as those in the production method of the present disclosure.

[Pulp cooking aid]
In one aspect, the present disclosure relates to a cooking aid comprising a Pluronic-type nonionic surfactant having an EO:PO ratio (weight ratio) of 55:45 to 85:15 and a weight average molecular weight of PO of 200 to 900. According to the pulp cooking aid of the present disclosure, in one or more embodiments, it is possible to produce pulp with a low kappa number while suppressing a decrease in yield. According to the pulp cooking aid of the present disclosure, in one or more embodiments, it is possible to achieve a kappa number reduction effect even with a lower alkali addition amount than when cooking is performed with a cooking liquor that does not contain a Pluronic-type nonionic surfactant. The Pluronic-type nonionic surfactant in the cooking aid of the present disclosure is the same as that in the production method of the present disclosure.

In one or more embodiments, the content of the Pluronic nonionic surfactant in the cooking aid of the present disclosure is 1% by weight to 50% by weight, and preferably 5% by weight to 40% by weight.

In one or more embodiments, the cooking aid of the present disclosure may contain water. In one or more embodiments, the water content in the cooking aid of the present disclosure can be determined according to the content of the Pluronic nonionic surfactant. In one or more embodiments, the blending ratio of water to the Pluronic nonionic surfactant (100 parts by weight) is 100 parts by weight to 2000 parts by weight, and preferably 200 parts by weight to 1200 parts by weight.

In one or more embodiments, the cooking aid of the present disclosure may further include an antifoaming agent and other additives.

The cooking aids of the present disclosure, in one or more embodiments, may be used in oxygen cooking for delignification (e.g., cooking performed in an oxygen cooker ( _O2 reactor) in an oxygen delignification process).

In one or more embodiments, the pulp cooking aid of the present disclosure can be used in the manufacturing method and cooking method of the present disclosure. Thus, in one or more embodiments, the pulp cooking aid of the present disclosure is a cooking aid for use in the manufacturing method or cooking method of the present disclosure.

The present disclosure further relates to one or more of the following embodiments.
[1] A method for producing chemical pulp, comprising the steps of:
The method includes subjecting a lignocellulosic material to alkaline or sulfite cooking using a cooking liquor that includes a Pluronic-type nonionic surfactant that is a polyoxyethylene polyoxypropylene block polymer;
the ratio (EO:PO) of oxyethylene groups (EO) to oxypropylene groups (PO) in the nonionic surfactant is 55:45 to 85:15 (weight ratio);
The weight average molecular weight of the oxypropylene group in the nonionic surfactant is 200 to 900.
[2] The method according to [1], further comprising adding the nonionic surfactant to the cooking liquor in an amount of 0.01% by weight to 1% by weight based on the bone dry weight of the lignocellulosic material.
[3] The method according to [1] or [2], wherein the weight average molecular weight of the nonionic surfactant is 500 to 3,000.
[4] A method for cooking lignocellulosic material, comprising alkaline cooking or sulfite cooking the lignocellulosic material using a cooking liquor containing a Pluronic-type nonionic surfactant which is a polyoxyethylene polyoxypropylene block polymer, comprising:
the ratio (EO:PO) of oxyethylene groups (EO) to oxypropylene groups (PO) in the nonionic surfactant is 55:45 to 85:15 (weight ratio);
The cooking method, wherein the weight average molecular weight of the oxypropylene group in the nonionic surfactant is 200 to 900.
[5] The cooking method according to [4], further comprising adding the nonionic surfactant to the cooking liquor in an amount of 0.01% by weight to 1% by weight based on the bone dry weight of the lignocellulosic material.
[6] The cooking method according to [4] or [5], wherein the weight average molecular weight of the nonionic surfactant is 500 to 3,000.
[7] A cooking aid for lignocellulosic material comprising a Pluronic-type nonionic surfactant which is a polyoxyethylene polyoxypropylene block polymer,
the ratio (EO:PO) of oxyethylene groups (EO) to oxypropylene groups (PO) in the nonionic surfactant is 55:45 to 85:15 (weight ratio);
The cooking aid, wherein the weight average molecular weight of the oxypropylene group in the nonionic surfactant is 200 to 900.
[8] The cooking aid according to [7], wherein the weight average molecular weight of the nonionic surfactant is 500 to 3,000.

The present disclosure will be explained in more detail below with reference to examples, but these are merely illustrative and the present disclosure is not limited to these examples.

[Cooking experiment]
A cooking test was carried out using 60 acacia mangium square timber (40mm x 20mm x 5mm) at an active alkali addition rate (AA) of 16%. The cooking liquor used was the one with the following composition containing the cooking aids shown in Table 1 below, and the liquor ratio (ratio of cooking liquor weight to bone dry weight of timber: liquor/timber) was 2.8 (L/kg). The cooking conditions were [40°C → 100°C (40min) → 163°C (50min) → 163°C (90min) → 100°C (15min, pressure release)]. After cooking, the chips were separated from the black liquor, and then disintegrated for 1.5 minutes in a disintegrator (the rotation speed started from 1500 rpm and increased to 2500 rpm), and then cleaned with a flat screen (10 cuts). In order to keep the temperature during pulping constant, the black liquor and the separated cooking chips were collected in a plastic cup and cooled to room temperature, and then pulped in sequence. The screened pulp was collected in a cloth bag connected to the outlet of the flat screen, rinsed five times with 2 L of stored water, and then dehydrated in a washing machine. The pulp obtained was measured for pulp consistency (dried overnight at 105°C), brightness, screening yield (yield), and kappa number (KN) by the following method. The concentration of the cooking aid added shown in Table 1 below was 200 ppm (0.02% by weight) per bone dry chip. In Table 1 below, Pluronic type (condensation type) means a Pluronic type nonionic surfactant of oxyethylene polyoxypropylene condensation type, and C.P. is the cloud point when made into a 1% by mass aqueous solution.
<Cooking liquor>
Composition: active alkali 16% by mass (based on the bone-dry weight of lignocellulosic material), sulfidity 28.3% by mass (based on the bone-dry weight of lignocellulosic material)
Active alkali: NaOH concentration + _Na2S concentration converted to _Na2O

[Cooking aid]
The cooking aids used were the chemicals shown in Table 1. In Examples 1 to 3 and Comparative Examples 1 to 3, an oxyethylene polyoxypropylene condensation type Pluronic nonionic surfactant (made to order) having the EO/PO ratio and weight average molecular weight shown in Table 1 was used. Mw in Table 1 refers to the weight average molecular weight. In Comparative Examples 4 to 6 and Reference Example 1, commercially available chemicals were used.

[Various analyses]
Pulp Consistency The obtained pulp was dried overnight at 105° C., and the weights before and after drying were measured, and the pulp consistency was calculated as the dry solid concentration.
- Whiteness
Handmade paper with a basis weight of 100 g/ ^m2 was prepared according to the method of JIS P8222 and measured using a Spectrophotometer (PF7000, manufactured by Nippon Denshoku Industries Co., Ltd.).
・Selection yield
The total bone dry pulp volume was divided by the bone dry volume of the lumber used, as shown in the following formula.
[Refining yield (%)] = total bone dry pulp volume ÷ bone dry pulp volume of square timber × 100
・Kappa number (KN)
The obtained pulp was used as a sample and measurements were carried out in accordance with JIS P8211.
・Digestion promotion effect ◎: "refining yield decrease of less than 0.1 or no decrease or increase" and "kappa number decrease of 1.0 or more"
〇: "Refining yield decrease of less than 0.1 or no decrease or increase" and "Kappa number decrease of less than 1.0"
△: "Reduced refinement yield" and "Reduction in kappa number less than 1.0"
×: "Decrease in refinement yield" and "Deterioration of kappa number"

The results are shown in Table 1 and Figure 2. In Table 1 and Figure 2, Δyield and ΔKN indicate the difference ([measurement result] - [blank]) between the yield and kappa number obtained in the above experiment and the result of a blank (AA: 16 mass%) in which cooking was performed in the same manner as in the above cooking experiment using cooking liquor containing no cooking aid. In other words, the larger the Δyield value on the + (plus) side (the higher it is in Figure 2), the more the yield is improved, and the larger the ΔKN value on the - (minus) side (the further it is on the left side in Figure 2), the lower the kappa number.

As shown in Table 1 and Figure 2, Examples 1 to 3 had a superior cooking promotion effect and were able to obtain pulp with a low kappa number compared to Comparative Examples 1 to 6. Also, the decrease in yield was suppressed. In other words, cooking was promoted and the quality of the obtained pulp was improved by cooking with a cooking liquor containing a Pluronic surfactant having an EO:PO ratio of 60:40 to 80:20 (weight ratio) and an oxypropylene group weight average molecular weight of 500 to 700.
Example 2 achieved a kappa number and yield comparable to those achieved when anthraquinone (50 ppm) was used as a cooking aid (data not shown).
In Reference Examples 2 and 3, cooking was carried out in the same manner as in the above cooking experiment, except that the cooking liquor was used with an active alkali addition amount of 16.5 mass% or 17 mass% and did not contain a cooking aid. As shown in Table 1, Examples 1 to 3 were able to lower the kappa number compared to Reference Example 1, in which the active alkali addition amount was 16.5 mass%, and were able to achieve a kappa number at a level similar to that of Reference Example 2, in which the active alkali addition amount was 17 mass%.
Therefore, by cooking with a cooking liquor containing a Pluronic surfactant having an EO:PO ratio of 55:45 to 85:15 (weight ratio) and an oxypropylene group weight average molecular weight of 200 to 900, it is possible to produce a chemical pulp with a low kappa number while suppressing a decrease in yield.

Claims (5)

A method for producing chemical pulp, comprising the steps of:
The method includes alkaline cooking the lignocellulosic material with a cooking liquor that includes a Pluronic-type nonionic surfactant that is a polyoxyethylene polyoxypropylene block polymer;
the ratio (EO:PO) of oxyethylene groups (EO) to oxypropylene groups (PO) in the nonionic surfactant is 55:45 to 85:15 (weight ratio);
The weight average molecular weight of the oxypropylene group in the nonionic surfactant is 200 to 900. The method of claim 1, further comprising adding the nonionic surfactant to the cooking liquor in an amount of 0.01% to 1% by weight based on the bone dry weight of the lignocellulosic material. The method according to claim 1 or 2, wherein the weight average molecular weight of the nonionic surfactant is 500 to 3,000. 1. A method for cooking lignocellulosic material, comprising alkaline cooking the lignocellulosic material with a cooking liquor comprising a Pluronic-type nonionic surfactant which is a polyoxyethylene polyoxypropylene block polymer,
the ratio (EO:PO) of oxyethylene groups (EO) to oxypropylene groups (PO) in the nonionic surfactant is 55:45 to 85:15 (weight ratio);
The cooking method, wherein the weight average molecular weight of the oxypropylene group in the nonionic surfactant is 200 to 900. 1. A cooking aid for alkaline cooking of lignocellulosic material comprising a Pluronic-type nonionic surfactant which is a polyoxyethylene polyoxypropylene block polymer,
the ratio (EO:PO) of oxyethylene groups (EO) to oxypropylene groups (PO) in the nonionic surfactant is 55:45 to 85:15 (weight ratio);
The weight average molecular weight of the oxypropylene group in the nonionic surfactant is 200 to 900.

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