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
• • 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

Definitions

• the present invention relates to the treatment of wood and more in particular to a method of continuously pretreating wood prior to the sulfite cooking process of the wood with lime milk.
• wood can be pretreated prior to being subjected to the sulfite cooking process so as to obtain a higher yield of cellulose products having improved parchmentizing properties.
• the wood or wood fibers or other cellulose-containing raw materials arepretreated with an aqueous alkali or alkaline earth substance.
• the pretreatment is carried out by first adding to the wood fibers, either in the cooking vessel or in another suitable container, several times the quantity of its proper Weight of aqueous alkali or alkaline earth'solutions.
• the Wood fibers are subjected to the effect of this solution of lye for a period of several hours with a view to impregnating and saturating the Wood as thoroughly as possible with the alkali or alkaline-earth lye.
• the impregnating process can be further improved by circulating the lye and subjecting the wood fibers to pressure or a vacuum treatment. After the impregnation process the excessive lye is removed.
• an index of saturation of 2.0 can be obtained.
• index of saturation it late be defined as the ratio of the amounts by weight of water contained in a determined amount byweight of theoretically dry wood after the impregnation to the weight of the dry wood. While it is thus possible, according to the known art, to obtain a very thorough impregnation, the impregnation process itself is time-consuming and, in addition, cannot be carried out continuously.
• the object of the present invention is thus achieved by adding milk of lime to the Wood fibers and agitating the Wood fibers, the quantity of the milk of lime being so chosen that after the treatment, one weight unit of the theoretically dry wood containsincluding the natural water contents of the woodnot more than one weight unit of water, and then leaving the thus imregnated wood for a predetermined periodand preferably several hours under the influence of the lime.
• the milk of lime should contain'an amount of CaO in "the range from 0.5 to of the theoretically dry wood. -Preferably,'the contents are in the'order of l to 2%.
• the milk of lime is replaced by solutions containing equivalent amounts of alkaline substances or ammonia.
• this pretreatment can be carried out, for example, by passing hogged chips through a rotating drum and simultaneously adding lime milk.
• the amount of lime milk added to the hogged chips is adapted to a liquid content of the wood in such a manner that after the treatment, the wood has an 'index of saturation of, for example, 0.8.
• the pretreatment can be further simplified by providing one or several conveyer belts. The hogged chips are moved by the conveyer belts, and when so moved are sprayed with milk of lime, preferably at those locations where the hogged'chips' are passing from one conveyer belt to another and are thus stirred and well mixed with the lime milk. While the pretreatment with conveyer belts is'very simple, it will be noted that the pretreatment with a rotating drum'is preferable in-as-much as better mixing effect is obtained;
• the wood chips thus provided with lime are then stored for at least one hour, or better several hours and thus are subjected to the influence of the lime milk. 'By several hours I wish to be understood a period of about five hours and more, for example two to fifteen hours,
• the storing time is selected from theirange of 5 to 15 hours.
• the method of the invention also offers the considerable advantage of diluting the acid used for the sulfite cooking to a far smaller extentthan :is the case with the known pretreating processes. This will now be explained in further detail.
• the known impregnating processes use an excessive amount of milk of lime, and subject the hogged chips to the influencethereof for at least one hour, in the presence of saturation of 2).
• pregnated wood chips can receive only 2.5 'times' the amount by weight of the weight ,ofthe wood, that is only 55% by weight of the normal amount of acid. Consement conditioning the cellulose'yield.
• impregnated wood is treated with a cooking acid in a known manner containing 6.3% and 1.1 CaO,"at
• the impregnation carried out according to the method of the invention results in an index of saturation, for example, 0.8, so that for one weight unit of wood there can be sup plied to the cooking vessel 3.7 parts by weight of acid;
• a further advantageous feature 'of the invention resides in the fact that the wood chips are subjected to the influence of the milk oflime fora considerable period of time, for example at least one hour, and preferably 5 to 15 hours. .It has been discovered and it will become further apparent from the following examples that the cellulose yield after the sulfite cooking subsequent to the impregnation carried out according to the invention rises COHSldl'flf bly in direct proportion to an increase of the period. of
• Example I Hoggedchips of fir wood having a liquid content of 10% are filled into a rotating cylindrical vessel.
• a milk of lime is prepared containing 12.5 grams of CaO per liter and 0.7 part by weight, with referenceto the absolutely theoretically dry weight of the. wood, is supplied to the Wood chips. After minutes the .liquid is completely increase in yield of cellulose.
• Example II g Example'pl. is repeated with the exception, that the milk of lime contains 25grarns CaOper liter and the im pregnated Wood contains 2.0% CaO.
• the sulfite cooking is effected with an. acid containing '5.5%' S0 and 1.1% CaO during 9 /1 hours at a super-atmospheric 'pressure 0 55 anda maximumtemperature of 129 C.
• Example 111 Example I is repeated with the-exception that the wood is treated with a milkof limecontaining per liter 37.5 grams CaO. After the impregnation, the wood contains 3.1% CaO; It is then stored for a period of twelve hours, during which time the lime is allowed to act'on the Wood chips, whereupon the Wood chips are digested with an acid containing :6% S0 and 0.84%
• the cellulose material obtained after the pregtreatnrentdescribed in Examples'l to ,3 has also greatly increased parchmentizing properties. It has been'found that there is a certainiproportionality between the increase of the yield and the improvement, of the parchmentizing property. Withother-wordawhere, as a consequence of the pretreating method of the inventiomthe cellulose yield has increased, the parchmentizing properties have also improved, vwiththe latter;i mprovement.1being so much more pronounced as. the yield increaseis higher.
• the additional yield with reference to untreated wood in percent of the weight of the pulp is 9.0.
• Example V Example I is repeated with the exception that for the impregnation of the hogged chips the lime is replaced by 0.7 part by weight of an ammonia solution containing 15 grams of ammonia per liter.
• the impregnation degree of the wood is 0.8, and after the impregnation it contains 1.2% ammonia (NH Thereafter the ammonia is allowed to act upon the hogged chips in a period of 12 hours, whereupon the sulfite cooking is effected according to Example I.
• the cellulose yield (in percent) of the wood is 58.0%, the Iohnsen-Noll number is 50.
• a process for the production of cellulose from fir wood comprising first pretreating the Wood by impregnation with an alkaline solution and then subjecting said pretreated wood to a sulfite digestion, the improvement which comprises discontinuing said impregnation when up to an amount by weight of the alkaline solution is absorbed in the wood, so that one part by weight of the theoretically dry wood contains at the end of the impregnation not more than one part by weight of water including the natural water content of the wood, the strength of said alkaline solution being equivalent to an amount of 0210 in the range of 0.5-5 of the theoretically dry wood; and storing said impregnated wood for at least one hour prior to introducing said wood into the sulfite digestion.
• the alkaline solution comprises a member of the group consisting of milk of lime, sodium hydroxide, and ammonia.

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• Chemical And Physical Treatments For Wood And The Like (AREA)

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ID=6927670

Family Applications (1)

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Citations (5)

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• 1959
  • 1959-05-12 DE DEA32025A patent/DE1098804B/de active Pending
• 1960
  • 1960-03-28 CH CH344660A patent/CH395724A/de unknown
  • 1960-04-01 FR FR18821A patent/FR1256711A/fr not_active Expired
  • 1960-05-11 US US28239A patent/US3177112A/en not_active Expired - Lifetime
• 1962
  • 1962-07-24 FR FR19812A patent/FR82035E/fr not_active Expired

Patent Citations (5)

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