US3661698A - Production of pulp by a multi-stage ammonium polysulphide pulping process - Google Patents

Production of pulp by a multi-stage ammonium polysulphide pulping process Download PDF

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US3661698A
US3661698A US864740A US3661698DA US3661698A US 3661698 A US3661698 A US 3661698A US 864740 A US864740 A US 864740A US 3661698D A US3661698D A US 3661698DA US 3661698 A US3661698 A US 3661698A
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polysulphide
liquor
pulp
chips
impregnation
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US864740A
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English (en)
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David W Clayton
Asahi Sakai
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Pulp and Paper Research Institute of Canada
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Pulp Paper Res Inst
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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
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D21C1/06—Pretreatment of the finely-divided materials before digesting with alkaline reacting compounds

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  • ABSTRACT In a process for the production of cellulosic pulp from lignocellulosic material which comprises impregnating said material in subdivided form with a polysulphide liquor containing ammonium hydroxide in an amount sufficient to maintain a pH of at least i 1.5 and at a temperature below that at which substantial decomposition of the polysulphide occurs, removing excess polysulphide from the material, heating the polysulphide impregnated material in the presence of am monia gas to stabilize the material, and subsequently cooking the material with sodium hydroxide containing cooking liquor to delignify the material.
  • FIG. 2 A 51 JFPOF POLYSULPHIDE CONSUMED ON WOOD FIG. 2
  • the present invention relates to the production of pulp in improved yield from ligno-cellulosic materials such as wood, straws and grasses by the polysulphide process.
  • the present invention relates to the production of cellulosic pulp in increased yield by a modification of the aforesaid polysulphide process in which the amount of polysulphide and alkali required is substantially reduced.
  • the subdivided wood or other ligno-cellulosic material is cooked in an aqueous solution of sodium hydroxide-sodium sulphide at a temperature of the order of 170 C. for the time required to produce a pulp in the required yield.
  • the resulting pulp contains lignin and carbohydrate in a ratio which is determined by the specific conditions of the pulping process i.e., the temperature cycle, the time, the liquor to wood ratio and the ratio of chemical to wood.
  • the ratio of carbohydrate to lignin in the pulp from a given material at a given yield is a quantity which varies within very narrow limits being virtually fixed by the nature of the process.
  • the aforesaid cooking is effected in the presence of polysulphide ion, suitably effected by adding sodium polysulphide or elemental sulfur to the cooking liquor and the pulping operation is carried out under appropriately modified conditions which are well known to those skilled in the art.
  • the polysulphide pulps which are obtained have a higher ratio of carbohydrate to lignin than the pulps obtained in the kraft or sulphate process at the same yield, due to the stabilization of the wood polysaccharides against alkaline degradation by the polysulphide ion.
  • pulp products of the aforesaid polysulphide process compare favorably with the pulps obtained in the conventional kraft or sulphate process and, in particular, pulps having the same Kappa number produced by the polysulphide process are usually darker in color, have easier beatability, have higher strength in burst and tensile, slightly lower strength in double fold and tear and have similar bleachability
  • the conventional single stage polysulphide process is subject to several problems.
  • the polysulphide sulfur charge is increased a much higher alkali charge is required for the required delignification because hydroxyl ions are consumed by the decomposition of the polysulphide ion to hydrosulphide and thiosulphate ions.
  • the rate of decomposition of the polysulphide ion increases with the temperature and becomes appreciable above 100 C. in the presence of hydroxyl ions and in a typical liquid phase pulping cycle most of the polysulphide is destroyed before the maximum temperature is reached.
  • the polysulphide charge can be better used by lowering the maximum temperature the practical minimum in a single stage process is about 160 C. below which the delignification rate is too slow to be of commercial use.
  • the two-stage process of the Japanese Patent although an improvement upon the single stage conventional polysulphide pulping procedure, still has the disadvantage that a substantial quantity of the polysulphide is destroyed in the stabilization stage without it reacting with the polysaccharides in the ligno-cellulosic materials. This is due to the relatively high temperature of 130 C. used in the stabilization and, although polysulphide decomposes more slowly at lower temperatures, it still decomposes fairly rapidly at 130 C. and if lower temperatures were used in the stabilization stage of the process of the Japanese Patent the reaction between the polysulphide and the polysaccharides would proceed too slowly to achieve maximum carbohydrate yield.
  • the decomposition of the polysulphide means a direct loss of chemical to the process and necessitates the installation of an expensive recovery system to regenerate the polysulphide for reuse in the stabilization of fresh ligno-cellulosic material and thus adds considerably to the cost of the pulp.
  • the impregnation is carried out so that the required amount of polysulphide ion is uniformly taken up in the subdivided lignocellulosic material without any substantial loss by decomposition.
  • the temperature and usually the pH of the material can be adjusted in order to effect the stabilization reaction for which optimum conditions depend upon the nature of ligno-cellua losic material, e.g. the wood species.
  • the conditions for stabilization are not limited by the necessity of protecting polysulphide ion from decomposition.
  • the essence of the invention in U.S. application Ser. No. 665,710 therefore is the capability of the process for the establishment of optimum conditions for a complete and uniform impregnation of the lignocellulosic material with the least loss of polysulphide decomposition followed by the maximum possible stabilization of polysaccharides before the alkaline delignification stage.
  • the impregnated ligno-cellulosic material is then subjected to stabilization which necessitates increasing the temperature above 100 C. and suitably above 120 C. in order to cause reaction to occur between the polysulphide and the ligno-cellulosic material.
  • the rate atwhich the polysulphide stabilizes the polysaccharides in the lignocellulosic material is much lower, at a' low pH of about 1 1, than at high pH of about 14 and according to one embodiment of the invention set forth in U.S. application Ser. No. 665,710, ammonia gas is added to the stabilization stage and the impregnated cellulosic material is heated with direct steam above 130 C.
  • ammonia gas is added to the stabilization stage and the impregnated cellulosic material is heated with direct steam above 130 C.
  • the pH within the ligno-cellulosic material is adjusted to a value at which the net loss of polysaccharides is at a minimum.
  • Such a process is specifically illustrated in Example II of U.S. application Ser. No. 665,710.
  • the stabilization stage of the process of the present invention then involves raising of the temperature of the impregnated ligno-cellulosic material suitably by steaming with the addition if necessary of further ammonia to provide optimum stabilization conditions therein and the delignification stage involves addition of sodium hydroxide of Kraft liquor in a similar manner as in U.S. application Ser. No. 665,710.
  • a process for the production of cellulosic pulp from ligno-cellulosic materials which comprises substantially completely impregnating said material in subdivided form with a polysulphide liquor containing no added sodium hydroxide at a pH below 12.5 and at a temperature below that at which substantial decomposition occurs; removing excess polysulphide from the impregnated material; stabilizing the impregnated material against alkaline degradation by increasing the temperature of said material and subsequently de-lignifying the stabilized material by cooking said material in a cooking liquor containing sodium hydroxide, the improvement which comprises efi'ecting impregnation of said material with a polysulphide liquor containing ammonium hydroxide in an amount sufficient to maintain a pH of at least about 1 1.5 and effecting stabilization by heating the impregnated material in the presence of ammonia gas under superatmospheric pressure.
  • the present invention has application to any ligno-cellulosic material, particularly those in the production of paper products, it has particular application to the treatment of wood such as softwood and thus, the present invention will be further described with reference to wood as the ligno-cellulosic material and, in particular, to wood chips representing the ligno-cellulosic material in subdivided form.
  • wood chips representing the ligno-cellulosic material in subdivided form.
  • the present invention is not limited to the treatment of wood chips.
  • the impregnation of the wood chips with the polysulphide liquor is according to the present invention effected at a temperature below that at which substantial decomposition of the' polysulphide ion takes place in the polysulphide liquor. It has been found experimentally that the polysulphide ion, particularly when in contact with wood decomposes to a substantial extent at temperatures above 110 C. and it is, therefore, according 'to the present invention suitable to effect the impregnation at temperatures below 110 C. and suitably below 100 C.
  • the temperature is suitably in the range 7090 C. and, more preferably in the range 90 C.which allows the impregnation to be effected at pressures less than about 20 psig and the impregnation time is suitably 30 to 60 minutes.
  • the polysulphide liquor may be a sodium polysulphide liquor as in the process of U.S. application Ser. No. 665,710. in a preferred embodiment of the present invention the polysulphide liquor is an ammonium polysulphide liquor (NH Swhich it is found promotes the impregnation of the wood chips particularly when in admixture with ammonium hydroxide in accordance with the present invention.
  • NH S ammonium polysulphide liquor
  • the impregnation of the chips with the liquor can be effected on either dry chips or water saturated chips, the latter being the preferred procedure as in U.S. application Ser. No. 665,710. If the chips are dry, impregnation can be brought about by forcing liquid into the empty capillaries in the fibers, carrying the chemicals with it, this being referred to as penetration. If the chips are moisture saturated no further entry of liquid is possible and ions must enter by diffusion after the liquid has enveloped the chips. In intermediate moisture contents both mechanisms contribute to the impregnation.
  • the impregnation of the polysulphide be effected upon wet chips of moisture content in excess of 100 percent based on dry wood and this highmoisture content is preferably produced, when the moisture content of the chips is initially too low, by soaking the chips in warm water for some time.
  • the impregnation of wet chips with the polysulphide can, of course, be effected at substantially atmospheric pressure whereas in using pressure in combination with dry chips it is necessary to use complicated apparatus involving pressure vessels, which, of course, is from a commercial point of view to be avoided.
  • moisture contents in excess 5 of 170 percent give difficulties in operating a continuous process unless expensive equipment to condense the excess of withdrawn liquor is installed and for practical purposes a moisture content in the range 100-160percent is preferred for impregnation under mild conditions.
  • the impregnation of the wet chips is suitably effected for a period of the order of k hour to 1 hour as it is found that in this range of times the wet chips can be impregnated with two-thirds of the quantity of the chemicals which can be introduced after four days.
  • the delignification of the stabilized chips is suitably carried out by adding soda or kraft liquor to the stabilized chips and cooking the chips at a temperature of 160 C. or higher.
  • a minimum temperature of 160 as aforesaid is usually required for the delignification but suitably this is from 170 C. to 175 C. in the liquid phase, the pressure suitably being from 100-l20'psig and the time suitably being from 40 to 70 minutes.
  • the chips were sealed grams per 1ner 'mpregnanon with polysulphlde P 15 h in a polyethylene bag and were stored in a cold room at 3 to generally sufficient for the process of the present invention 0 C101. from 2 to 5 weeks Before being subjected to cooking and above 40 grams per liter there is no substantial advantage any free water was drained away by keeping the wet chips in a to be gained. Thus, the amounts of sodium and tot l p9 y wire mesh basket (60 mesh) for 1 hour.
  • a Th liquor-t -wogd ratio in the impregnation stage is number of these aliquots were subjected in an impregnation suitably in the range of 2.5:1 to 4:1 as above the ratio of 4:1 an Stage to heating with 1305 of an aqueous ammonium infinite bath effect is approached where a two-fold increase P y p P ammonium hydroxide at 3 P of about 12 in the ratio leads only to a 10 percent increase in impregnation and a liquor to wood ratio of The hhpreghatod o P were under the same conditions.
  • the ammonium polysulphide solution used in the impregnap y p I c tion stage was prepared by injecting hydrogen sulphide gas
  • the stabil zation may be effected by heating the iminto 2N ammonium hydroxide solution and then dissolving the pr gn tcd Chips tinder pressure after withdrawal of the excess required amount of elemental sulphur in this solution at C. of polysulphide liquor with direct steam to a temperature of at 60
  • the composition of the solution is set forth in Table 1. least 170 C. and preferably 170-175 C.
  • FIG. 1 is a plot of Kappa numbers against total at different polysulphide consumptions shown i for the three different processes
  • FIG. 2 is a plot of total percent pulp yield against polysulphide consumption at Kappa number 30, and
  • FIG. 3 is a plot similar to FIG. 1 of screened pulp yield against Kappa number for different p consumption.
  • the chips were steam-purged at I20 C twice for periods of three minutes, admixed with the polysulphide liquor at 20 C at a pressure of 100 psig for 60 minutes at a liquor to wood ratio at 5 to I and the temperature was then raised over 90 minutes to 170 C and maintained at that temperature for a period of 55 to 70 minutes.
  • the cooking condi- 40 tions and the results obtained are shown in the following Table IV from which graph I-C was obtained.

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US864740A 1969-10-08 1969-10-08 Production of pulp by a multi-stage ammonium polysulphide pulping process Expired - Lifetime US3661698A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4130457A (en) * 1973-06-04 1978-12-19 Union Camp Corporation Method of pulping with polysulfide
US5041192A (en) * 1988-09-16 1991-08-20 University Of South Florida Supercritical delignification of wood
US20090126883A1 (en) * 2007-11-20 2009-05-21 Jianer Jiang Use of polysulfide in modified cooking
EP2537979A1 (en) * 2011-06-23 2012-12-26 Metsä Fibre Oy Method of producing cellulose pulp
US20190226142A1 (en) * 2018-01-19 2019-07-25 Jim Constantacos Method for improved pulping using an environmentally friendly pulping aid

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2944928A (en) * 1957-09-20 1960-07-12 Kibrick Method of preparing paper pulp

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2944928A (en) * 1957-09-20 1960-07-12 Kibrick Method of preparing paper pulp

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4130457A (en) * 1973-06-04 1978-12-19 Union Camp Corporation Method of pulping with polysulfide
US5041192A (en) * 1988-09-16 1991-08-20 University Of South Florida Supercritical delignification of wood
US20090126883A1 (en) * 2007-11-20 2009-05-21 Jianer Jiang Use of polysulfide in modified cooking
US7828930B2 (en) 2007-11-20 2010-11-09 International Paper Company Use of polysulfide in modified cooking
US20110155335A1 (en) * 2007-11-20 2011-06-30 International Paper Company Use of polysulfide in modified cooking
EP2537979A1 (en) * 2011-06-23 2012-12-26 Metsä Fibre Oy Method of producing cellulose pulp
RU2606867C2 (ru) * 2011-06-23 2017-01-10 Андритц Ои Способ изготовления целлюлозной массы
US20190226142A1 (en) * 2018-01-19 2019-07-25 Jim Constantacos Method for improved pulping using an environmentally friendly pulping aid

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FI51114B (enrdf_load_html_response) 1976-06-30
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NO130020B (enrdf_load_html_response) 1974-06-24

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