EP0468016B1 - Process for preparing kraft pulp - Google Patents

Process for preparing kraft pulp Download PDF

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Publication number
EP0468016B1
EP0468016B1 EP91903366A EP91903366A EP0468016B1 EP 0468016 B1 EP0468016 B1 EP 0468016B1 EP 91903366 A EP91903366 A EP 91903366A EP 91903366 A EP91903366 A EP 91903366A EP 0468016 B1 EP0468016 B1 EP 0468016B1
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EP
European Patent Office
Prior art keywords
cellulosic material
carried out
temperature
cooking
liquor
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Revoked
Application number
EP91903366A
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German (de)
English (en)
French (fr)
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EP0468016A1 (en
Inventor
Panu Olavi Tikka
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Metso Paper Pori Oy
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Sunds Defibrator Pori Oy
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D21C1/06—Pretreatment of the finely-divided materials before digesting with alkaline reacting compounds
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/0021—Introduction of various effluents, e.g. waste waters, into the pulping, recovery and regeneration cycle (closed-cycle)

Definitions

  • the present invention relates to a process for preparing kraft pulp. More particularly, the present invention relates to processes for preparing kraft pulp in which cellulosic material is treated with white or fresh liquor for dissolving the lignin therein. The present invention specifically relates to the pretreatment of the lignin-containing material before the lignin digestion step.
  • FI-A-29611 describes a pretreatment process utilizing hydrogen sulfide under elevated pressure.
  • SE-A-309530 relates to a pretreatment process utilizing liquid hydrogen sulfide at a pH of between 4 and 10.
  • Polysulfide treatment has also been proposed as a second pretreatment step.
  • the kraft process has been developed by means of different technical processing means.
  • the need to save energy has led to new solutions, the most important of which have been continuous cooking processes (see, e.g., FI-A-54155).
  • the equipment used in such continuous cooking processes can include the use of several co- and countercurrent circulations, as well as separate impregnation vessels.
  • US-A-2639987 discloses a process for the preparation of pulp from wood comprising charging a digester with wood chips, adding to the digester black liquor, heating the charge to a temperature between 160°C and 175°C for 6-30 minutes, discharging the exhausted liquor from the digester, than adding to the digester a liquor comprising white liquor and delignifying the wood.
  • this process is applicable to the soda as well as to the kraft process, it is particularly designed for digesting eucalyptus chips with soda (sodium hydroxide) without sulfur chemicals.
  • the cooking is carried out in two steps; first in black liquor at 160-175°C for 6-30 minutes to neutralize 80-100% of the residue alkali; and then in white liquor containing an unusually small concentration of alkali (NaOH 15-20%/wood).
  • the purpose of the method is to utilize the residue alkali of the spent cooking liquor for delignifying reactions. In the first step indeed same reactions take place as in the second step.
  • Alkaline Pulping represents a general description of the alkaline pulping processes.
  • the objects of this invention and improvements in the kraft pulp process have now been provided by means of a process for the preparation of kraft pulps from lignin- containing cellulosic materials, which comprise impregnating the cellulosic material with spent alkaline cooking liquor at a temperature of between about 20 and 100°C, heating the impregnated cellulosic material at a temperature of between about 135 and 155°C, and delignifying the heated cellulosic material with fresh alkaline cooking liquor.
  • impregnating of the cellulosic material with spent alkaline cooking liquor employs liquor having a pH of between about 11.5 and 13.5, and preferably between about 12.5 and 13.5.
  • heating of the impregnated cellulosic material is carried out for a period of from about 1 to 30 minutes, whereby the pH of the spent alkaline cooking liquor impregnated into the cellulosic material is decreased to between about 9 and 11, and preferably to between about 9.5 and 10.5.
  • the spent and fresh alkaline cooking liquor comprises sodium hydroxide.
  • the spent alkaline cooking liquor has a residual sodium hydroxide content of between about 4 and 20 grams of sodium hydroxide per liter, and more preferably between about 6 and 15 grams of sodium hydroxide per liter.
  • the step of heating the impregnated cellulosic material is carried out at a temperature of between about 135 and 155°C. Preferably this step is carried out for a period of between about 10 and 30 minutes.
  • the cellulosic material is hardwood and the step of delignifying the heated cellulosic material is carried out using an H-factor of between about 900 and 1000, in order to produce a readily fiberized paper pulp.
  • the cellulosic material is softwood and the step of delignifying the heated cellulosic material is carried out using an H-factor of between about 400 and 700, in order to produce a readily fiberized paper pulp.
  • the step of delignifying the heated cellulosic material is carried out at a temperature of between about 180 and 190°C.
  • the principal advantage of the process of the present invention is that digestion of the lignin with white liquor is greatly facilitated by means of this process.
  • the chips are pretreated with spent cooking liquor, or so-called black liquor. This pretreatment takes place in two steps. In the first step the chips are impregnated with the spent liquor, and in the second step they are reacted with it.
  • the chips are essentially filled with the spent liquor.
  • the temperature of this impregnation step must be below 100°C in order to avoid reaction therewith on the surface of the chips. In practice temperatures of from about 20 to 100°C are utilized.
  • the time of this impregnation step should be from at least about 10 minutes, and preferably between about 15 and 20 minutes. Impregnation times of more than about 30 minutes are unnecessary.
  • the pH of the spent liquor is between about 11,5 and 13,5, preferably between about 12.5 and 13.5, and the residual alkali content is from about 4 to 20 g NaOH/l, and preferably between about 6 and 15 g NaOH/l.
  • the pretreatment reaction or heating step which follows the impregnation step is carried out at an elevated temperature of from about 135 to 155°C.
  • the reaction time depends on the temperature which is utilized, and is generally from about 1 to 30 minutes. Preferably, a reaction time of from about 10 to 30 minutes is utilized.
  • this heating step the residual chemicals in the black liquor react with the wood material, and alkali is consumed.
  • the pH within the chips is thus decreased to from about 9 to 11. It is believed that in this altered chemical environment sulfur compounds react with the lignin, and thereby render it more reactive in the digestion step which follows thereafter. It is also assumed that hydrogen sulfide reacts with the end groups of carbohydrates in the wood, thus protecting them against alkaline decomposing reactions.
  • Pretreatment of the chips in this manner renders the subsequent digestion step substantially easier.
  • the severity of the digestion conditions which are required is generally determined by the so-called H-factor.
  • H-factors In a normal kraft process of, e.g., Scandinavian softwood, H-factors of from about 1600 to 1800 are required. In the present process, H-factors can be diminished by about 400 to 1000. This means that the overall digestion time can be significantly shortened. on the other hand, it has also been observed that exceptionally high digestion temperatures, such as from about 180 to 190°C, can be employed in the present process. This can lead to further shortening of the digestion time. In conventional kraft processes, the digestion step generally takes about one hour. In accordance with the present invention, howeyer, digestion times of about one-half hour are now possible.
  • An additional advantage of the present process is the increased selectivity of the delignification reaction. This, in turn, leads to higher yields and superior pulp quality, or to a lower consumption of cooking chemicals.
  • the digestion reaction can now also be run for a longer period of time, and a lower lignin concentration can thus be achieved than is the case in conventional processes.
  • the pulp which is obtained thereby thus requires less bleaching, which, in turn, decreases the amount of harmful compounds which are discharged from the bleach plant into the waste waters therefrom.
  • the digester In batch cooking techniques, all of the steps can be carried out in the same reactor, i.e., the digester.
  • the contents of the digester are heated to a temperature in the range of the reaction temperature in the case of ( i ) conventional batch processes, by means of the digester circulation being equipped with a heat exchanger, or by direct steam injection, and ( ii ) in case of low energy batch cooking, using the displacement technique, by displacing the colder impregnation black liquor with hotter black liquor for the purpose of carrying the process heat back to the digester.
  • Another embodiment of this invention utilizing batch digesters is to impregnate the chips with the black liquor in the context of chip filling in separate equipment.
  • the reaction stage would thus appear as the first step in the digester after chip filling, and could be very effectively carried out by the use of direct steam subsequent to the draining of the impregnation black liquor, or by displacing the impregnation/filling media black liquor by hotter black liquor.
  • continuous impregnation is carried out while charging the digester and is combined with batch cooking techniques, thus resulting in ( i ) compensation for the extra time spent with the black liquor stage, and ( ii ) reduction of the total cooking cycle time due to the greater speed of the cooking step.
  • the present invention can also be carried out in connection with continuous cooking processes.
  • the continuous digester equipment presently being used including separate impregnation vessels and various co- and countercurrent circulations, effectively segregate the cooking process into several steps, in which the present invention can include starting the process with black liquor and without white liquor.
  • the chips are fed into the gester or impregnation vessel along with the black liquor, the temperature is elevated to the reaction range by heating with the aid of liquor circulation-heat exchanger.
  • the white liquor is then fed into the digester, displacing the black liquor, the temperature is again increased by means of a circulation-heat exchanger and the rest of the process is carried out in the conventional manner.
  • An alternative continuous process is to carry out the black liquor treatment stage as a countercurrent operation.
  • continuous cooking to kappa numbers of about 30 generally requires a reaction time of from 60 to 90 minutes in the cooking temperature range. If extended cooking to lower kappa numbers of between about 23 and 25 are required, an extra cooking stage, and an additional 60 minutes of cooking time is generally required, thus totaling at least two hours of cooking time.
  • the acceleration of the delignification step of this invention however, the cooking time, and the size of the cooking zone in the continuous digester, can be cut in half, therefore also rendering the equipment cheaper, and its operation far simpler.
  • a forced circulation 20 liter digester was charged with pine chips in an amount corresponding to 3kg of absolutely dry wood, and 15 liters of spent black liquor was added (pH 13.2, residual alkali concentration 7 g NaOH/l as effective alkali), so that the liquid ratio was 5:1.
  • the digester was then closed, and pressurized with nitrogen in order to permit the taking of samples and the equalization of impregnation.
  • the circulation was initiated, and the temperature of the digester was elevated from 20°C to 70°C in five minutes by means of a heat exchanger, and it was then held at that temperature for 55 minutes. Samples were then taken from the circulation, cooled down to 25°C, and their pH measured. The procedure and development of the pH in the Cook are shown in FIG. 1.
  • An industrial batch digester having a capacity of 140 m 3 was filled with pine chips and spent black liquor (pH 13.4) from previous cookings. The temperature was elevated to 140°C, and maintained at that temperature for 15 minutes. The pH thus decreased to 11. White liquor was then added so that the alkali dosage was 18.2% of effective alkali, given as Na 2 O. The temperature was then raised to 170°C, and digestion continued to the desired level of delignification reduction, by altering the digestion time. The digester was then discharged, H-factor utilized registered, and the pulp was analyzed.
  • FIG. 3 shows the H-factor in each digestion as a function of the kappa number of the pulp obtained therein.
  • This Cook was carried out in the manner of a conventional batch Cook, without black liquor impregnation and treatment stages:
  • the alkali charge was 21% effective alkali as Na 2 O per wood H-factor 2000 Pulp kappa number 71.1 Pulp viscosity 905
  • Temperature of the black liquor treatment was 145°C.
  • the time of black liquor treatment was 20 minutes.
  • the alkali charge was 18.2% effective alkali as Na 2 O per wood H-factor 1000 (Example 2, Cooks 5, 6: 1080) Pulp kappa number 28.1 (Example 2, Cooks 5,6: 25.4)
  • the tear-tensile relationship of the pulp was analyzed in order to evaluate the pulp strength. At a useful tensile index of 70, the tear index was 16, which equals the value found on curve "A" in FIG. 4 in Example 2, applying a normal cooking temperature and black liquor treatment. This slightly exceeded that of a normal cooking temperature with no black liquor treatment.
  • FIG. 6 sets forth a comparison between cooking temperature and time profiles for the Cook in this Example, and that of Cook Nos. 5 and 6 in Example 2, representing normal cooking temperatures.
  • the pulp conditions prior to the blow were determined by hanging baskets filled with the same chip material inside the digester. After the blow, pulp which had not been blown could thus be recovered from these baskets, and compared to samples of the blown pulp.
  • the analysis carried out was in terms of a so-called strength delivery, which is the percentage of the pulp strength as tear index at a tensile index of 70 measured in the blown pulp as compared to that of non-blown pulp in the basket.
  • Cooks were carried out with a black liquor treatment stage as described in Example 2, Cook Nos. 4-6, discharged by: hot blow, directly from full cooking temperature; cold blow, after cooling displacement to under 100°C; and pump discharge after cooling displacement.

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  • Inorganic Chemistry (AREA)
  • Chemical & Material Sciences (AREA)
  • Paper (AREA)
  • Diaphragms For Electromechanical Transducers (AREA)
  • Mechanical Treatment Of Semiconductor (AREA)
  • Polysaccharides And Polysaccharide Derivatives (AREA)
  • Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
  • Inorganic Insulating Materials (AREA)
  • Noodles (AREA)
  • Compositions Of Oxide Ceramics (AREA)
  • Holo Graphy (AREA)
  • Nonmetallic Welding Materials (AREA)
  • Iron Core Of Rotating Electric Machines (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)
EP91903366A 1990-02-09 1991-02-11 Process for preparing kraft pulp Revoked EP0468016B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FI900663A FI93866B (fi) 1990-02-09 1990-02-09 Menetelmä sulfaattimassan valmistamiseksi
FI900663 1990-02-09
PCT/FI1991/000043 WO1991012368A1 (en) 1990-02-09 1991-02-11 Process for preparing kraft pulp

Publications (2)

Publication Number Publication Date
EP0468016A1 EP0468016A1 (en) 1992-01-29
EP0468016B1 true EP0468016B1 (en) 1996-08-14

Family

ID=8529860

Family Applications (1)

Application Number Title Priority Date Filing Date
EP91903366A Revoked EP0468016B1 (en) 1990-02-09 1991-02-11 Process for preparing kraft pulp

Country Status (14)

Country Link
EP (1) EP0468016B1 (fi)
JP (1) JP2900091B2 (fi)
AT (1) ATE141351T1 (fi)
AU (1) AU639304B2 (fi)
BR (1) BR9104333A (fi)
CA (1) CA2049322C (fi)
DE (1) DE69121332T2 (fi)
ES (1) ES2091319T3 (fi)
FI (1) FI93866B (fi)
NO (1) NO178935C (fi)
NZ (1) NZ236941A (fi)
PT (1) PT96713B (fi)
WO (1) WO1991012368A1 (fi)
ZA (1) ZA91958B (fi)

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE469842C (sv) * 1992-01-21 1996-01-15 Sunds Defibrator Ind Ab Blekning av kemisk massa med peroxid
NZ247276A (en) * 1992-04-06 1994-12-22 Westvaco Corp Production of papermaking fibre of low lignin content from recycled high lignin waste paper; mixtures with fresh pulp and products produced therefrom
FI970254A (fi) * 1997-01-22 1998-07-23 Ahlstrom Machinery Oy Menetelmä ja laitteisto massan keittämiseksi
FI20002586A (fi) * 2000-11-24 2002-05-25 Metso Paper Inc Alkalinen eräkeittomenetelmä kuitumateriaalille
FI20002587A (fi) * 2000-11-24 2002-05-25 Metso Paper Inc Alkalinen keittomenetelmä kuitumateriaalille
KR20110123184A (ko) 2010-05-06 2011-11-14 바히아 스페셜티 셀룰로스 에스에이 높은 알파 용해 펄프 제조를 위한 방법 및 시스템
AR091998A1 (es) 2012-05-03 2015-03-18 Annikki Gmbh Procedimiento de preparacion de celulosa con baja concentracion de lignina
KR102143773B1 (ko) * 2018-10-25 2020-08-12 한국세라믹기술원 리그노셀룰로오스 바이오매스를 이용한 부분결정성 활성탄의 제조방법 및 상기 부분결정성 활성탄을 이용한 슈퍼커패시터의 제조방법
KR102157512B1 (ko) * 2018-11-16 2020-09-18 한국세라믹기술원 리그노셀룰로오스 바이오매스를 이용한 구형의 다공성 활성탄 제조방법 및 이를 이용한 슈퍼커패시터의 제조방법

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE101369C1 (fi) *
US1687076A (en) * 1927-10-12 1928-10-09 Venning D Simons Process for cooking wood chips by the alkaline process of pulp manufacture
US2639987A (en) 1947-07-09 1953-05-26 Ass Pulp & Paper Mills Two-stage pulping process
US4578149A (en) * 1981-03-05 1986-03-25 Fagerlund Bertil K E Process for digesting cellulosic material with heat recovery

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
J.P. Casey "Pulp and Paper; Chemistry and Chemical Technology" 3rd edition, vol. I, 1980, John Wiley & Sons, New York, pages 377, 392-397, 411-416 ("Alkaline Pulping"). *

Also Published As

Publication number Publication date
AU7218991A (en) 1991-09-03
NO178935B (no) 1996-03-25
PT96713A (pt) 1991-10-31
JPH04505485A (ja) 1992-09-24
NO178935C (no) 2000-06-26
FI900663A (fi) 1991-08-10
NO913873D0 (no) 1991-10-02
AU639304B2 (en) 1993-07-22
CA2049322C (en) 2002-08-20
EP0468016A1 (en) 1992-01-29
ATE141351T1 (de) 1996-08-15
NZ236941A (en) 1993-10-26
CA2049322A1 (en) 1991-08-10
JP2900091B2 (ja) 1999-06-02
DE69121332D1 (de) 1996-09-19
WO1991012368A1 (en) 1991-08-22
PT96713B (pt) 2001-05-31
ES2091319T3 (es) 1996-11-01
BR9104333A (pt) 1992-04-21
NO913873L (no) 1991-10-02
ZA91958B (en) 1991-11-27
FI93866B (fi) 1995-02-28
FI900663A0 (fi) 1990-02-09
DE69121332T2 (de) 1997-03-13

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