Classifications

• • 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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
  • D21C3/022—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes in presence of S-containing 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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/22—Other features of pulping processes
  • D21C3/26—Multistage processes
  • D21C3/266—Multistage processes the same pulping agent being used in all stages
• • 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
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

• This invention relates to the making of chemi-mechanical pulp from hardwood for wood-containing printing paper, especially wood-containing fine paper.
• Pine paper traditionally is manufactured from a mixture of short-fibred and long-fibred chemical pulp. In order to improve the opacity of the paper and to increase its bulk, conventionally a certain amount of bleached groundwood pulp was mixed into the stock. The term wood- -containing fine paper is used when the amount of ech- anical pulp exceeds 10%.
• CTMP H peroxide-bleached chemi-mechanical pulp of hardwood
• CTMP ⁇ -pulp very high requirements are made on the properties of the CTMP ⁇ -pulp, because the paper in addition to high ISO-brightness and good opacity preferably also should have high bulk and simultaneously high stremgth and low roughness. For coated papers also low porosity is required. It is especially important, that these papers have a uniform surface structure.
• CTMP H -pulp in wood-containing fine paper it must be refined to a drainage resistance of 100-200 ml CSF, and it must be possible to bleach it to a brightness of 82-85$ ISO, which is a very high brightness for a mechanical pulp.
• the energy consumpt- ion at the refining thereby is relatively high, and so is the chemical consumption at the bleaching. This applies particularly to dark hardwood with high density and various types of eucalyptus.
• An extensive equipment in the form of means for drainage and washing is re ⁇ quired for the bleaching.
• the present invention implies, that this equipment can be simplified and the consumption of chemicals and electric energy be reduced without deteriorating the pulp quality.
• the hardwood in the form of chips is impregnated in one or two steps at a temper ⁇ ature below 80°C with 15-40 kg NaOH and 0-30 kg Na 2 S0, per ton pulp. Thereafter a refining under pressure is carried out in such a way, that the temperature of the chips prior to the refining does not exceed 8 ⁇ °C for a period longer than 10 seconds. Subsequent bleaching of the pulp is carried out with peroxide in one or two steps, and additionally a minimum of 15 kg NaOH is charged so that the total amount of NaOH charged is 30- 80 kg per ton pulp. Thereafter refining of the pulp is carried out in a second step.
• the invention implies that the brightness and light-scatt- erii ⁇ g coe ficient of the pulp is maximized and at the same time the energy consumption at the refining is minimized.
• the strength of the pulp is determined by the total of the alkali charge during the impregnation and peroxide bleaching steps.
• the alkali charge during the impregnation step shall be determined only with regard being paid to the shives content and fibre distribution number and disregarding the pulp_-_strength obtained by the alkali charge during the bleaching step.
• the refining in the second step is carried out with partially washed pulp, i.e. pulp con- taining residual alkali and residual peroxide from the bleaching, in order to minimize the energy demand at the refining and to be able to utilize the refining step as a third bleaching step carried out at a very high temper ⁇ ature, whereby it shall be possible to obtain highest brightness with a certain peroxide charge.
• the total peroxide charge at the bleaching shall be 30-50 kg peroxide per ton pulp, preferably 30-40 kg for light wood types and 40-50 kg for dark ones.
• Fig. 1 shows the ISO-brightness after peroxide bleaching as a function of the NaOH-charge during the impregnation step
• Fig. 2 shows the tensile strength of the pulp as a funct ⁇ ion of the total NaOH-charge.
• the pretreatment of the hardwood in the form of chips of eucalyptus saligna is carried out by washing, atmos ⁇ pheric steaming and so-called PREX-impregnation with a NaOH/Na p SO,-solution with pH 13.
• PREX-impregnation 20 kg NaOH and 20 kg Na- j SO., per ton are supplied to the chips.
• the chemicals are allowed to react for 30 minutes with the chips which hold 50 C.
• the pulp is diluted and dewatered to 35$ pulp concentrat ⁇ ion and thereafter mixed with complex former, prefer ⁇ ably EDTA, at pH 5 a thereafter diluted and again press- ed to 3 $ dry matter content.
• complex former prefer ⁇ ably EDTA
• the pulp is thereafter peroxide bleached in two steps, the first one at 15-18$ pulp concentration with residual peroxide from the washing following after the second bleaching step.
• a ⁇ er the first bleaching step which is carried out at 70 C for 30 minutes, the pulp is again washed and pressed to 35$ dry matter content, at which content the fresh bleaching chemicals are mixed into the pulp.
• the pulp is bleached for 120 minutes at 70°C with 0 kg peroxide, 25 kg NaOH and 30 kg sodium silicate Na p SiO-, per ton pulp, whereafter the pulp is washed by dilution with 4,5 parts washing water and pressing to 35$ dry matter content.
• the pulp is refined in a pressurized disc refiner,together with reject from the screen room, with 600 kWh/ton, with 3-5 kg/cm steam pressure and simultaneous addition of 5 kg peroxide per ton pulp to the refiner inlet.
• the energy input at this refining should be 400-800 kWh/ton.
• the pulp is latency treated at 3.5$ pulp concentration and 70 C, screened in pressurized screens in two steps and thereafter pumped to storage before being used in a paper mill.
• the pulp has the properties as follows:
• FIG. 1 is shown how the brigltness varies with the NaOH- -charge during the impregnation step at three different peroxide charges.
• Pulp I was manufactured from chips, which had been impregnated with 25 kg NaOH per ton pulp. With a peroxide charge of 45 kg per ton pulp it is then possible to obtain a brightness of above 80$ ISO. Pulp II was manufactured from chips impregnated with 50 kg NaOH per ton pulp.In spite of bleaching with a peroxide charge as high as 45 kg per ton pulp, it is not possible to increase the brightness higher than to about 77$ ISO.
• the original NaOH- -charge was 20 kg per ton pulp.
• the brightness could there be increased by peroxide bleaching to 82.5$ ISO.
• a lower NaOH-charge at the chip impregnation results in a decrease of the strength properties of the pulp. It was found, however, that the pulp strength within certain limits depends only on the total NaOH-charge during the impregnation and peroxide bleaching steps. During the impregnation step, therefore, NaOH is charged in an amount of 15-40 kg per ton pulp in order to ensure the necessary shives content and fibre distribution number. Additional NaOH in an amount of at least 15 kg per ton pulp to a total amount of 30-80 kg per ton pulp is charg ⁇ ed first in connection with the peroxide bleaching after the first refining.
• the NaOH-charge can be said, that heavy and dark wood types, such as eucalyptus, require more alkali for the development of their strength than wood types, which are Oiighter and brighter, such as asp and poplar.
• the NaOH-charge for the heavier and darker wood types should be 20-40 kg and for the lighter and brighter ones 15-25 kg per ton pulp.
• the total NaOH-charge should be 40-80 and, respectively, 30-50 kg per ton pulp.
• Fig. 2 is shown how the tensile strength of the pulp changes with the total amount of NaOH charged and peroxide bleaching with 4 kg peroxide per ton pulp. Freeness 125 ml CSF.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Paper (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20373326

Family Applications (1)

Country Status (8)

Cited By (3)

Families Citing this family (1)

Citations (4)

Family Cites Families (1)

• 1988
  • 1988-09-14 SE SE8803244A patent/SE460124B/sv not_active IP Right Cessation
• 1989
  • 1989-07-07 EP EP19890908892 patent/EP0434696A1/en not_active Withdrawn
  • 1989-07-07 WO PCT/SE1989/000395 patent/WO1990002835A1/en not_active Application Discontinuation
  • 1989-07-07 BR BR898907631A patent/BR8907631A/pt unknown
  • 1989-07-07 AU AU40374/89A patent/AU616999B2/en not_active Expired - Fee Related
  • 1989-08-11 CA CA 608079 patent/CA1334240C/en not_active Expired - Fee Related
  • 1989-09-13 ES ES8903114A patent/ES2017145A6/es not_active Expired - Lifetime
• 1991
  • 1991-03-13 FI FI911242A patent/FI911242A0/fi unknown

Patent Citations (4)

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