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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/22—Other features of pulping processes
  • D21C3/222—Use of compounds accelerating the pulping 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
  • D21C1/04—Pretreatment of the finely-divided materials before digesting with acid 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
  • D21C3/22—Other features of pulping processes
  • D21C3/26—Multistage processes

Definitions

• This invention relates to a process for producing pulp from a lignocellulosic-containing material. More particularly, this invention relates to a process for producing dissolving pulp from a lignocellulosic-containing material.
• Other terms synonymous with dissolving pulp are chemical cellulose and special high alpha pulp.
• Two processes are in general use for the manufacture of dissolving pulp viz:
• prehydrolysis acidic pretreatment
• PH-NS-AO prehydrolysis - neutral sulphite - anthraquinone process
• This prehydrolysis step performs essentially the same function as the prehydrolysis step prior to the Kraft (Sulphate) pulping method for the manufacture of dissolving grade pulp; while the neutral sulphite-anthraquinone delignification step is essentially the same as the process also known as the semi-alkaline sulphite-anthraquinone (SAS-AQ) process, first reported at a technical conference in 1979 by Raubenheimer, S and Eggers, S.H., (both being research workers employed by SAPPI LIMITED, the present applicant herein) viz the 11th European ESPRA Meeting, Maastricht, The Netherlands, during May 1979.
• SAS-AQ semi-alkaline sulphite-anthraquinone
• a process for producing dissolving grade pulp including - applying a prehydrolysing step to a lignocellulosic-containing material for example hardwood. partly dissolving the lignin contained in the prehydrolysed material (- a pulping step); and carrying out an alkali extraction step.
• alkali About 2% to 5%, preferably about 3%, by mass of alkali may be used to carry out the alkali extraction step.
• the alkali used may preferably be sodium hydroxide.
• the alkali extraction step may be carried out at a temperature of about 50°C to 100°C, preferably about 70°C to 80°C, for a period sufficient to give optimal lignin removal.
• a process for reducing the lignin content (as expressed by the Kappa number) of unbleached pulp intended for dissolving grade pulp manufacture including applying an alkali extraction step to the pulp.
• alkali About 2% to 5%, preferably 3%, by mass of alkali may be used to carry out the alkali extraction step.
• the alkali used may preferably be sodium hydroxide.
• the alkali extraction step may be carried out at a temperature of about 50°C to 100°C, preferably 70°C to 80°C, for a period sufficient to give optimal lignin removal.
• Spent liquor from the pulping step may be removed from a digester, treated with alkali, and re-introduced to the digester to lower the Kappa number of the pulp and/or to improve evaporation of the spent liquor.
• the digester may be operated at a temperature > 100°C and at elevated pressure.
• the alkali used may preferably be sodium hydroxide.
• the invention extends to a dissolving grade pulp whenever produced by a process as herein described and/or exemplified.
• Prehydrolysis and pulping were carried out under laboratory conditions on run-of-mill (ENSTRA) Eucalyptus wood chips. The prehydrolysis conditions and yields are shown in Table 1 hereunder.
• the Kappa number from cook no. C1 was relatively high.
• Bleach number B1 was done before the positive effect of an extraction step after pulping was established. Because of the high unbleached Kappa number, bleach chemical charges were extremely high. Both the alpha-cellulose content and the pulp yield looked promising. Bleach number B2 was done using an extracted unbleached pulp with a kappa number of 17,6. Both the alpha cellulose content and pulp yield were high.
• the spent hydrolysis liquor from run no. P8 was titrated against standard NaOH solution in order to get an indication of the caustic soda consumption of such liquor. This would be relevant in the case where the prehydrolysis step is done in the same vessel or digester as the pulping step and the acidity of the liquor remaining after draining of the bulk of the prehydrolysis liquor has to be neutralized when adding pulping chemicals. Neutralization required 2,4g NaOH per litre of prehydrolysis liquor.
• the initial concentration of Na2SO3 (as NA2O) at a charge of 17% at a L/W ratio of 3,5/l was 48,6 g/l.
• cook number C5 was done at the same initial concentration as the other cooks but at a much higher charge (-L/W ratio increased to 5,3/l).
• the anthraquinone charge was also increased to 0,2% (on timber) and the time at top temperature was increased to 4 hours.
• the Kappa number could be lowered to 28,7 but this is still relatively high for a bleachable hardwood pulp. See hereunder under the heading "Extraction Step".
• Cook number C11 was done in order to simulate the procedure when doing prehydrolysis, pulping and the extraction step(s) in a single vessel (- batch digester, no washing between steps), as follows:
• Spent pulping liquor from cook number C6 was titrated against NaOH in order to determine the amount of caustic soda necessary to raise the pH to 11 (the approximate pH at which all NaHCO3 will be converted to Na2 CO3). This figure came to 12g NaOH per litre of spent pulping liquor.
• the final Kappa number of 13,4 was in line with figures obtained doing the three steps separately with washing between each step.
• the NaOH necessary to raise the pH of the remaining pulping liquor to 11 came to about 4,5% on O.D. pulp.
• Hydrolysed material was soaked for 30 minutes in water after treatment before washing and spin drying.
• C17 was done using original wood material which had not been subjected to a prehydrolysis step.
• the chemical charge was increased to 18% Na2SO3 (as Na2O) and 4,5% Na2CO3 (as Na2O) keeping the anthraquinone charge and other conditions as above.
• the Kappa number drop obtained from the unhydrolised pulp (Cook C17) on extraction also indicates the different nature of the lignin in this pulp compared to the lignin in pulp which had been hydrolised. If this material had been obtained by applying a hydrolysis step prior to the pulping step, the Kappa number drop on extraction would have been more pronounced considering the unextracted Kappa number of this pulp. The above results were obtained from pulp which had been well washed after the pulping step in order to demonstrate the positive effect of an alkaline extraction step.
• the preferred procedure would be to drain the digester after the prehydrolysis step of the prehydrolysis spent liquor. (This liquor would be used for recovery and beneficiation of products dissolved and extracted from the wood).
• the pulping chemicals Na2SO3, Na2 CO3, and Anthraquinone
• NaOH sodium acetate
• the spent liquor would be pumped from the digester.
• Alkali NaOH
• the digester would then be added to this liquor and reintroduced to the digester followed by circulation for a period. This would complete the cook.
• An oxygen bleaching step also proved effective in further lowering the Kappa number to acceptably low levels prior to full bleaching.
• Full bleaching of such pulps required fairly low charges of chlorine-containing chemicals, thereby providing a process which has a low pollution potential.
• "Non polluting" bleach chemicals like ozone and peroxide could also be considered.

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• 1991
  • 1991-02-08 PT PT96722A patent/PT96722A/pt not_active Application Discontinuation
  • 1991-02-08 BR BR919100565A patent/BR9100565A/pt unknown
  • 1991-02-11 ZW ZW11/91A patent/ZW1191A1/xx unknown
  • 1991-02-11 RU SU914894714A patent/RU2037594C1/ru active
  • 1991-02-11 FI FI910655A patent/FI910655A/fi unknown
  • 1991-02-12 AU AU70987/91A patent/AU643746B2/en not_active Ceased
  • 1991-02-12 NZ NZ237098A patent/NZ237098A/en unknown
  • 1991-02-12 CA CA002036311A patent/CA2036311A1/en not_active Abandoned
  • 1991-02-12 MW MW01/91A patent/MW191A1/xx unknown
  • 1991-02-12 EP EP91400355A patent/EP0442806A1/en not_active Withdrawn
  • 1991-02-13 BR BR919100592A patent/BR9100592A/pt unknown

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