JP3029043B2 - Cooking method for lignocellulosic material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for cooking lignocellulosic materials, and more particularly, to the modification of alkaline cooking of lignocellulosic materials by adding a cyclic keto compound (cyclic keto compound-based cooking aid). It relates to alkaline cooking.

[Conventional technology]

The mainstream of industrial pulp production methods from lignocellulosic materials such as wood, which has been conventionally industrially performed, is an alkaline cooking method using an alkaline cooking liquor, and in particular, a kraft method (sodium sulfate) using a sodium sulfide-containing cooking liquor. Law)
Has been implemented on a large scale because of the balance between pulp strength, pulp yield, and ease of recovery of chemicals in pulp production.

In recent years, A. Hartler of the Royal University of Technology in Sweden (KTH) and A. Teder of the Forestry and Forestry Research Institute (STFI) aim to improve the problems of the alkaline cooking method, especially the kraft method, for example, to improve the demand for further improvement in pulp strength. Suggest the possibility of reducing residual lignin while maintaining the viscosity of unbleached pulp [Svensk Papperstidn., 81 (15), 483 (197
8), Tappi, 62 (7), 49 (1979)]. The alkaline cooking method having delignification selectivity is generally called a modified alkaline cooking method (hereinafter sometimes referred to as an MCC method).

And this modified alkaline cooking method, in the permeation vessel, and in each digester zone of the digester, always replenish fresh cooking liquor, optimize the alkali concentration, carry out co-current cooking and countercurrent cooking inside the digester In other words, in other words, the point at which the alkali concentration in the permeation vessel (permeation stage) is lowered by circulation of the permeate, and in the cooking liquor at the stage where cooking is completed by countercurrent cooking (ie,
..The characteristic feature is that the alkali concentration of the black liquor is lowered, and the viscosity of the obtained pulp is about 100 dm ³ / kg compared to the conventional digestion when measured at the same kappa number in the MCC method. A higher value is obtained, in other words, 5-7 points for N-wood (coniferous) and 3-4 points lower for L-wood (hardwood) in kappa number after cooking without loss of pulp strength and viscosity. It is known that the merit of this MCC method is maintained in the subsequent bleaching step. (See Pulp & Paper Times, August 1990, pp. 55-59.) The modified alkaline digestion will be described below with reference to the system diagram using a two-reactor type continuous digester shown in FIG. 3 attached below. The lignocellulosic material, specifically wood chips 1, is supplied to an open-air heated chip bin 2, heated and degassed in a steaming vessel 3, and then sent by a high-pressure feeder 4 to the top of a permeation vessel 6 through a conduit 5. Be paid. On the other hand, the main branch stream of the cooking liquor supplied from an alkaline cooking liquor (hereinafter referred to as cooking liquor) conduit 17 is supplied to the top of the permeation vessel 6 through a conduit 18. In the high-pressure feeder 4 the wood chips and the extract flowing in the extract conduit 7 from the top of the permeation vessel 6 are mixed, and this mixture is then fed through the conduit 5 to the top of the permeation vessel 6. The wood chips filled at the top of the infiltration vessel 6 descend together with the cooking liquor, during which a delignification reaction is partially started.

A strainer 39 is provided at an intermediate portion of the permeation vessel 6, and an extract from the strainer 39 is supplied to an extract conduit 40.
To the vicinity of the strainer 39 inside the infiltration vessel 6. The wood chips and the cooking liquor that passed through the strainer 39 reached the bottom of the permeation vessel 6 and
Is fed to the top of the digester body 8 through a transfer circulating fluid outgoing conduit 37 installed from the bottom of the digester 8 to the top of the digester 8. And seepage vessel 6
Can be referred to as permeation zone I in terms of the function with the following digestion zones A, B, C and washing zone D. On the other hand, the cooking liquor branched from the cooking liquor introduction pipe 17 passes through a cooking liquor branch pipe 19, further branches and passes through a cooking liquor branch pipe 20, and is provided from the top of the digester 8 to the bottom of the permeation vessel 6. Circulating fluid flowing in the circulating fluid return line 36
22 and supplied to the bottom of the permeation vessel 6. The heater 16 is installed in the middle of the transfer circulating fluid return line 36, and the heater 16 is heated by the medium-pressure steam 35 and the circulating fluid 22 is heated.

The digester main body 8 is roughly divided into four zones (zones) having different functions from the top to the bottom: an upper digestion trim zone A, an upper digestion zone B, a lower digestion zone C, and a washing zone D. In order to define the zones, a strainer 9 is provided at the boundary between the upper cooking trim zone A and the upper cooking zone B, a strainer 10 is provided at the boundary between the upper cooking zone B and the lower cooking zone C, and the lower cooking zone C and the washing zone. A strainer 11 is provided at the boundary with D, and a strainer 12 is provided below the washing zone D, that is, near the bottom of the digester 8.

The extract extracted from the strainer 9 installed in the lower part of the upper digestion trim zone A passes through the extract conduit 38 and the transfer circulating liquid return conduit 36 provided from the top of the digester 8 to the bottom of the permeation vessel 6. Combined with the flowing circulating fluid 22.

The partially delignified wood chips descending from the upper digestion trim zone A enter the upper digestion zone B, where the wood chips are co-digested and the delignification reaction proceeds. The digested black liquor extracted from the strainer 10 provided in the lower part of the upper digestion zone B is transferred to the recovery step (not shown) through the extracted black liquor conduit 30.

The wood chips that have advanced from the upper digestion zone B and have undergone some delignification (digestion) are then converted to the lower digestion zone C.
And in this zone, the wood chips that have undergone delignification are subjected to countercurrent cooking,
The delignification reaction proceeds further. This lower cooking zone C
In the strainer installed at the bottom of this zone
The extract extracted from 11 is combined with the cooking liquor flowing through the branch pipe 21 further branched from the cooking liquor branch pipe 19 in the extract liquid conduit 24, and supplied by the medium pressure steam pipe 33 by the heater 14 provided in the flow path. Heated by medium-pressure steam. This circulating liquid is supplied via a circulating liquid conduit 27 in the lower part of the lower cooking zone, near the strainer 11. In this zone, the wood chips that have undergone delignification to some extent descend from the lower part of the strainer 10 toward the upper part of the strainer 11, during which time the cooking liquor supplied from the circulating fluid conduit 27 near the strainer 11 was replenished. The circulating liquid rises toward the strainer 10, and the delignification reaction proceeds further by the countercurrent cooking. strainer
The circulating liquor rising towards 10 becomes used cooking liquor, ie black liquor, which is mixed with the black liquor in the upper cooking zone B and transferred via the extraction black liquor conduit 30 to a recovery step (not shown).

The wood chips that have undergone further delignification by the countercurrent cooking in the lower cooking zone C descend into the washing zone D below the strainer 11. In this zone, the washing liquid introduced through the washing liquid conduit 29 at the bottom of the washing zone D, just above the bottom of the digester 8 rises towards the strainer 11. On the other hand, the extract extracted by the strainer 12 passes through the extract liquid conduit 25, and is heated by the medium-pressure steam supplied by the medium-pressure steam pipe 34 to the heater 15 installed in the flow path and washed through the circulating liquid conduit 28. The circulating liquid supplied near the strainer 12 provided at the lower part of the zone D is combined with the washing liquid supplied by the washing liquid conduit 29 and rises toward the strainer 11 to finish the delignified wood in this zone. The chips (pulp) are countercurrently washed. The washed pulp is sent through a cooking pulp discharge pipe 31 to a washing machine (not shown). In the steaming vessel 3, the pressure is 0.5 to 2.0 kg / cm ² (gauge pressure), the temperature is about 110 ° C. to 130 ° C., and the top pressure in the infiltration vessel 6 is 12.0 to 1
4.0kg / cm ² (gauge pressure) temperature is about 110 ~ 130 ℃,
The partially delignified wood chips from the seepage vessel 6 have a kappa number of about 100 to 160.

In the digester body 8, the temperature in the upper digestion trim zone A is 145 to 165 ° C., and the upper digestion zone B
In the lower digestion zone C, the temperature is 150-170 ° C.
In the washing zone D, the extract extracted from the strainer 12 is heated by a heater 15 to a temperature of about 170 ° C.
The circulating fluid flowing through 28 is heated to 140-150 ° C.

The top pressure of the main body of the digester 8 is generally maintained at 10 to 13 kg / cm ² (gauge pressure). The temperature of the pulp discharged through the cooking pulp discharge pipe 31 is maintained at 75 to 95 ° C. The temperature of the black liquor discharged from the extraction black liquor conduit 30 is maintained at 150 to 170 ° C. Cooking liquid introduction pipe 17
Is supplied to the top of the permeation vessel 6 by the branch pipe 18 and to the bottom of the permeation vessel 6 by the branch pipe 20 of the branch pipe 19. The cooking liquor supplied by the branch pipes 18 and 20 is finally combined with the wood chips passing through the transfer circulating liquid outflow conduit 37 and fed to the top of the digester 8. Further, the cooking liquor flowing through the other branch pipes 21 of the branch pipes 20 of the branch pipes 19 is supplied to the lower cooking zone C at a lower portion, near the strainer 11, by a conduit 24, a heater 14,
It is supplied through a circulating fluid conduit 27.

Assuming that the cooking liquor supplied from the cooking liquor introduction pipe 17 is 100, the distribution ratio of the cooking liquor is 50 to 90% to the branch pipe 18, and
9 is supplied 10-50%. The cooking liquor introduced into the branch pipe 19 is further distributed by 5 to 45% by the branch pipe 20 and 5 to 45% by the branch pipe 21. As a result, 50 to 90% of the cooking liquor introduced from the cooking liquid introduction pipe 17 is obtained. % Of the cooking liquor is fed to the permeation vessel 6 via the inlet pipe 18, and 5 to 45% of the remaining 50 to 50% of the cooking liquor are fed to the upper cooking trim zone A via the inlet pipe 19, and 5 to 45% of the cooking liquor % Is generally distributed and supplied to lower cooking zone C.

FIG. 4 shows another embodiment of the modified alkaline cooking method. The difference from FIG. 3 is that the strainer 39 in the infiltration vessel 6 is used.
The extraction liquid conduit 40 through which the extraction liquid flows from the cooking liquid branch pipe 19
The cooking liquor introduced by the branch pipe 42 is introduced, the cooking liquor is not introduced into the transfer circulating liquid return line 36, and the extraction from the strainer 9 installed below the upper cooking trim zone A. The liquid is an extract conduit
23, is heated by the medium-pressure steam supplied by the medium-pressure steam pipe 32 by the heater 13 provided in the flow path, and supplied to the lower part of the upper digestion trim zone A and the vicinity of the strainer 9 through the circulating liquid conduit 26. And the extract is not combined with the circulating fluid flowing through the transfer circulating fluid return conduit 36.

Although FIGS. 3 and 4 show embodiments in which the washing zone D is provided inside the digester, this washing zone can be provided outside the digester 8 if necessary. Needless to say.

Since the above-mentioned conventional modified alkaline digestion method comprises an infiltration vessel and a digester, it is generally used in a two-reactor continuous digester (Two Vessel Type Co.).
ntinuous Digestor).

By the way, a modified alkaline digestion method by continuous operation using a real reactor shown in FIG. 3 of a two-reactor type continuous digester,
Specifically, when I tried the modified craft cooking method,
The modified kraft cooking method, which belongs to the modified alkaline cooking method by allocating the cooking liquor, certainly reduces the bleaching chemical and drainage load of unbleached pulp, but increases the cooking temperature and increases the cooking liquor per lignocellulosic material. That a new problem arises.

In order to explain the above-mentioned problems in the modified alkaline cooking method, one of the present inventors has conducted a modified alkaline cooking of a lignocellulose material using an alkaline cooking liquor. Based on the above, a method of cooking by adding 0.001 to 1.0% by weight was proposed.

More specifically, an infiltration vessel is installed in front of the digester, and the inside of the digester runs from the top to the bottom, and the upper digestion trim zone A, the upper digestion zone B, the lower digestion zone C, and optionally the washing. A zone D is provided. A two-reactor continuous type in which co-current cooking is performed in the upper cooking trim zone A and the upper cooking zone B, countercurrent cooking is performed in the lower cooking zone C, and washing is performed in the washing zone D. In the digestion method using a digester, 50-90% of the alkaline cooking liquor containing the cyclic keto compound introduced into the cooking system or the permeation vessel, 5-45% is in the cooking trim zone A, and 5-45% is in the lower part. Cooking with an alkaline cooking liquor supplied to cooking zone C and containing 0.001 to 1.0% by weight of a cyclic keto compound based on lignocellulosic material (Japanese Patent Application No. 2-235) No. 563 (JP-A-4-11)
9184)).

FIG. 2 shows a basic device series of this method. This equipment is temporarily piped to the actual two-reactor continuous digester shown in Fig. 3 (Oji Paper Co., Ltd., Kasugai Mill, operation in February 1989, production capacity NUKP800T / day), and the cooking liquor shown in Fig. 4 The introduction pipe 42 was installed in the line 40 from the strainer 39 of the permeation vessel 6 to the extraction liquid conduit 40. Further, a strainer 9 → extract liquid conduit 23 → heater 13 → circulation conduit conduit 26 line was provided in the upper digestion trim zone as shown in FIG. 4, and a digester branch pipe 44 was connected to the extract conduit 23. With this piping, the branch pipe 21 of the cooking liquor was further branched into a branch pipe 43 and a branch pipe 44, and the branch pipe 43 was connected to the pipe 24 in the lower cooking zone. A cyclic keto compound introduction tube 45 was provided in the cooking liquor introduction tube 17.
FIG. 2 shows a system diagram of an apparatus provided with such piping.

By the above-mentioned method, that is, the modified alkaline cooking method in which the cyclic keto compound is added through the cyclic keto compound introducing pipe 45, the amount of the cooking liquor added and the pulp yield were improved as compared with the conventional method. In addition, pulp quality (pulp viscosity, pulp strength) has been improved, and as a result, the side effect of improving papermaking speed has been achieved, but the cyclic keto compound, which is an expensive cooking aid, has been used more efficiently. Thus, there is a problem in improving the pulp yield and further improving the pulp quality.

[Problems to be solved by the invention]

The present invention has been made to solve the above problems in the modified alkaline cooking method using a cyclic keto compound as a cooking aid, and an object of the present invention is to provide a method for efficiently using a cyclic keto compound.

It is a further object of the present invention to provide an improved method of achieving a reduced cooking temperature in a modified alkaline cooking process, and another object of the present invention is to use an alkaline cooking liquor per lignocellulosic material in a modified alkaline cooking process. Another object of the present invention is to provide an improved method for achieving a reduction in the amount, and to provide an improved method for achieving an improved pulp yield in a modified alkaline cooking method.
Yet another object of the present invention is to provide an improved method for achieving further improvement in pulp strength obtained by the modified alkaline cooking method, and still other objects will be apparent from the following description.

[Means for solving the problem]

The present inventors have modified alkaline cooking method in which the lignocellulose material is cooked by adding the entire amount of the cyclic keto compound to the alkaline cooking liquor first introduced into the cooking system, that is, the alkaline cooking liquor containing the cyclic keto compound introduced into the cooking system. Of 50
9090% is fed to the infiltration vessel, 5-45% to the upper cooking trim zone A and upper cooking zone B, 5-45% to the lower cooking zone C, and the cyclic keto compound is added to the lignocellulosic material at 0.001%. In the method of cooking with an alkaline cooking liquor containing up to 1.0% by weight, the place of addition of the cyclic keto compound was examined in a multiplicity manner, and found to be in the digester co-current cooking section (upper cooking trim zone A and / or upper cooking zone) The present invention has been completed based on the finding that the problem is solved all at once by mainly supplying the cyclic keto compound to the alkaline cooking liquor to be introduced and conducting the cooking.

The digestion method of the lignocellulosic material of the present invention that achieves the above-mentioned object has an upper digestion zone A, an upper digestion trim zone A, in which an infiltration vessel is installed at an upper portion or a previous stage of the digester, and the inside of the digester extends from the top to the bottom. A cooking zone B, a lower cooking zone C, and a washing zone D are provided. In the upper cooking trim zone A and the upper cooking zone B, cocurrent cooking is performed. In the lower cooking zone C, countercurrent cooking is performed. 1 or 2 where cleaning is performed
In the cooking method using a reactor-type continuous digester, 50-90% of the alkaline cooking liquor introduced into the cooking system is introduced into the permeation vessel, and 5-45% is introduced into the upper cooking trim zone A and the upper cooking zone B. ~ 45% is supplied to the lower cooking zone C and an alkaline cooking liquor containing 0.001 to 1.0% by weight of the cyclic keto compound based on lignocellulosic material is fed to the upper cooking trim zone A and / or the upper cooking zone B for cooking. It is characterized by doing.

To summarize the present invention, the alkaline cooking liquor used in the modified alkaline cooking method, soda cooking method,
The chemicals used in the Kraft cooking method (sulfate method), the polysulfide cooking method, the alkaline sulfite cooking method, and the sodium carbonate cooking method can be used, but the two-reactor shown in FIG. 3 is preferable. It is a kraft cooking method and a polysulfide cooking method using a mold continuous digester, and has a sulfuration degree of 5 to 75%, preferably 5 to 50%. The effective alkali addition rate of the cooking liquor described above is 5 to 30%, preferably 10 to 20%.

Examples of the cyclic keto compound used in the present invention include benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthrenequinone and a nuclear-substituted quinone-based compound such as an alkyl, alkoxy, amino, nitro, hydroxy or halogen or carboxy derivative, sulfonic acid Salts or carboxylates are suitable. Hydroquinone-based compounds which are reduced forms of the quinone-based compounds are also used. It is appropriately selected from tautomers of the hydroquinone compound and a mixture of any of the above compounds. Tautomers of the above compounds include 10-hydroxy-anthrone, 1- and 2-alkyl-10-hydroxy-anthrone, 1- and 2-amino-10-hydroxy-anthrone, 1- and 2-hydroxy-10 -Hydroxy-anthrone, 1- and 2-halo-10-hydroxy-anthrone and any mixtures of the aforementioned anthrone compounds.

The cyclic keto compound is further selected from the group consisting of a 9,10-diketohydroanthracene compound and a 9,10-dioxyhydroanthracene compound obtained as a stable compound as an intermediate in an anthraquinone synthesis method by the Diels-Alder method. One or more compounds can be used.

Examples of the 9,10-diketohydroanthracene-based compound include, for example, 1,4-dihydro-9,10-diketoanthracene, 1,2,3,4-tetrahydro-9,10-diketoanthracene, 4,4a, 9a-tetrahydro-9,10-diketoanthracene, 2-ethyl-1,4,4a, 9a-tetrahydro-9,10-
Diketoanthracene, 2,3-dimethyl-1,4,4a, 9a-tetrahydro-9,10-diketoanthracene, 1,3-dimethyl-1,4,4a, 9a-tetrahydro-9,10-diketo Anthracene, 1-methyl-1,2,3,4-tetrahydro-9,10-diketoanthracene, 1,2,3,4,5,8-hexahydro-9,10-
Diketoanthracene, 1,4,4a, 5,8,8a, 9a, 10a-Octahydro-9,10-diketoanthracene, 2,3,6,7-tetramethyl-1,4,4a, 5,8 , 8a, 9a, 10a-octahydro-9,10-diketoanthracene, 1,2,3,4,5,6,7,8-octahydro-
Preferred is a mixture of 9,10-diketoanthracene, and 2,6- and 2,7-diethyl-1,4,4a, 5,8,8a, 9a, 10a-octahydro-9,10-diketoanthracene. Is a compound selected from unsubstituted and lower alkyl-substituted Diels-Alder adducts of naphthoquinone and benzoquinone, and from the viewpoint of effect and economy, 1,4-dihydro-9,10-diketoanthracene, 1,4, 4a, 9a-Tetrahydro-9,10-diketoanthracene and 1,4,4a, 5,8,8a, 9a, 10a-octahydro-9,10-diketoanthracene are suitable.

As the 9,10-dioxyhydroanthracene-based compound, 1,4-dihydro-9,10-dioxyanthracene,
4,5,8-tetrahydro-9,10-dioxyanthracene,
1,4,5,8,8a, 10a-Hexahydro-9,10-dioxyanthracene and the like, and sodium and potassium salts of 1,4-dihydro-9,10-dioxyanthracene can also be used.

In the present invention, the cyclic keto compound is used in an amount of 0.001 to 1.0% by weight, preferably 0.005% by weight, based on the lignocellulose material.
It is usually added to the cooking liquor, taking into account the liquor ratio (cooking liquor / lignocellulosic material) to be 0.001 to 1.0% by weight based on the lignocellulose material. The cyclic keto compound may be mainly added to the cooking liquor introduced into the co-current cooking section (upper cooking trim zone A and / or upper cooking zone B) of the digester.

Various lignocellulosic materials can be used to practice the pulping method of the present invention, for example, lignocellulosic materials for pulp production include softwood chips, hardwood chips, sawdust, and non-wood cellulose materials such as bagasse, kenaf , Straw, reeds and other annuals.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

Example Temporary piping for the actual two-reactor type continuous digester shown in FIG. 3 (Oji Paper Co., Ltd., Kasugai Mill, started operation in February 1989, production capacity NUKP 800T / day), was used to make a branch pipe 18 for the cooking liquor.
Was connected to the extract conduit 40. Further, a strainer 9 → extract liquid conduit 23 → heater 13 → circulating liquid conduit 26 line was provided in the upper digestion trim zone as shown in FIG. 4, and a digest liquid branch pipe 44 was connected to the extract liquid conduit 23.
With this piping, the branch pipe 21 of the cooking liquor is divided into a branch pipe 43 and a branch pipe 44.
And the branch pipe 43 is connected to the extract liquid conduit of the lower digestion zone.
Connected to 24. Further, a cooking ketone introduction pipe 17 is provided with a cyclic keto compound introduction pipe 45, and further, the cooking ketone branch pipes 18, 18 ', 20, 43, and 44 correspond to the cyclic keto compound introduction pipes 46, 47, 48, 50, respectively. 49
Was provided. FIG. 1 shows a system diagram of an apparatus provided with such piping. The installation position of the cyclic keto compound introduction tube 45 is, as described above, the addition position of the cyclic keto compound in the invention of Japanese Patent Application No. 2-235563. In the present invention, the cyclic keto compound is mainly placed in the introduction tubes 48 and / or 49. Addition, other introduction pipe 4
5, 46, and 50 carried out the modified Kraft cooking using the closed apparatus shown in FIG. And a pipe for introducing the cyclic keto compound
The compound is fed to upper cooking trim zone A and / or upper cooking zone B by introduction from 48 and / or 49.

The cooking liquid division ratio, the top pressure of the permeation vessel 6, the temperature condition, the top pressure condition of the digester 8, the upper cooking trim zone A, the upper cooking zone B, the lower cooking zone C, and the temperature condition of the washing zone D are as follows. The results are shown in Table 1.

The comparative example shows a conventional MCC method in which a cyclic keto compound is not added and a method in which the compound is added through a cyclic keto compound introduction tube 45, that is, a method of Japanese Patent Application No. 2-235563. The division ratio of the cyclic keto compound in Examples and Comparative Examples is the same as the division ratio of the cooking liquor.

Pine wood in Comparative Examples 1 and 2, and Examples 1 to 3, beech wood in Comparative Examples 3 and 4, and Examples 4 to 6, Comparative Examples 5 and 6,
In Examples 7 to 9, Douglas fir was cooked.

As the cyclic keto compound, 9,10-anthraquinone (AQ) is used in Examples 1 to 3, and disodium salt (DDA) of 1,4-dihydro-9,10-dioxyanthracene is used in Examples 4 to 10. did. Tables 2 to 4 show, as locations where the cyclic keto compound was added, infiltration zone I, upper digestion trim zone A, upper digestion zone B, lower digestion zone C, and inlet pipe positions 45, 46, 47, 48, 49,50 are also shown.

Regarding the physical properties of the pulp, selected pulp (unbleached) from which debris has been removed canadian freeness 500cc with a PFI mill
Beaten, was measured with a sheet having a basis weight of 60 g / m ² was handsheet according to TAPPI test method T205 _OS -71 (JIS P8209) to. In addition, about each test method, it performed according to the following method.

Kappa number TAPPI test method T236hm-85 Pulp viscosity TAPPI test method T230om-82 Whiteness JIS P8123 Also, the following measurement is based on the strength test method of paper pulp (JIS P8
In accordance with 210), the tear length was measured using each device of JIS P8113 specific rupture JIS P8112 specific tear JIS P8116.

Regarding the bleaching property test, the selected pulp from which the residue was removed was subjected to C (chlorine) -E (caustic soda) -H (hypo) -D (chlorine dioxide) in the usual order.

 The results are shown in Tables 2 to 4.

The temperatures and times in Tables 2 to 4 used the following values.

The temperature is the average of the cooking temperatures of the upper cooking trim zone A and the lower cooking zone C.

Time is upper cooking trim zone A + upper cooking zone B +
Total value of each cooking time in the lower cooking zone C.

From the comparison with Examples 1 to 9 and Comparative Examples 1 to 6, the cyclic keto compound of the present invention is mainly introduced into the co-current digester (upper digestion trim zone and / or upper digester) of the digester by the introduction pipes 48 and / or 49. The modified Kraft digestion by adding the cyclic keto compound to the cooking liquor initially introduced into the digestion system is compared with the invention of Japanese Patent Application No. 2-235563, ie, the method in which the cyclic keto compound is added through the introduction pipe 45. It is clear that the effect is remarkable.

Further, it goes without saying that the present invention can be applied to a modified alkaline cooking method using a single-reactor continuous digester.

〔The invention's effect〕

As is clear from the above description, the amount of cooking liquor can be reduced by the modified alkaline cooking method in which the cyclic keto compound is mainly added to the co-current cooking section (upper cooking trim zone and / or upper cooking zone) of the digester. Thus, an improvement in pulp yield was achieved. In addition, there is a secondary effect that pulp quality (pulp viscosity, pulp strength) is improved, and as a result, paper making speed is improved, and the present invention greatly contributes to the paper pulp industry.

[Brief description of the drawings]

FIG. 1 is a system diagram of an apparatus for carrying out the modified alkaline cooking method of the present invention, and FIG. 2 is a system diagram of an apparatus used for the cooking method of lignocellulosic material of Japanese Patent Application No. 2-235563. , FIG. 3 and FIG. 4 are system diagrams of an apparatus for performing the modified alkaline cooking method. 1 in the figure: wood chips, 6: seepage vessel, 8: digester, 9, 10, 11, 12, 39 ... strainer, I ...
... infiltration zone, A ... upper cooking trim zone, B ... upper cooking zone, C ... lower cooking zone, D ... washing zone, 1314, 15, 16 ... heater, 17 ... cooking liquid introduction pipe, 1
8,18 ', 19,20,21,43,44 …… Cooking liquid branch pipe, 45,46,47,4
8,49,50… Cyclic keto compound introduction pipe, 29… Washing liquid introduction pipe, 30… Extraction black liquor pipe, 31… Cooking pulp discharge pipe

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-216289 (JP, A) JP-A-4-119184 (JP, A) JP-A-55-62289 (JP, A) JP-A-4-216 209883 (JP, A) JP-A-4-209885 (JP, A) JP-A-4-209886 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D21C 3 / 00-3 / 02

Claims (1)

(57) [Claims] 1. An infiltration vessel is disposed at an upper part or a preceding stage of a digester, and an upper cooking trim zone, an upper cooking zone, a lower cooking zone and a washing zone are provided from the top to the bottom of the digester. A cooking method using a one- or two-reactor continuous digester in which an upper cooking trim zone and an upper cooking zone perform co-current cooking, a lower cooking zone performs counter-current cooking, and a washing zone performs washing. In the, 50-90% of the alkaline cooking liquor introduced into the cooking system,
5-45% is fed to the upper cooking trim zone and upper cooking zone, 5-45% to the lower cooking zone, and the cyclic keto compound is added to the lignocellulosic material at 0.001-1.0%.
A method for cooking lignocellulosic material, comprising feeding an alkaline cooking liquor containing% by weight to an upper cooking trim zone and / or an upper cooking zone for cooking.