US3092535A - Sulphite pulping process - Google Patents

Sulphite pulping process Download PDF

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Publication number
US3092535A
US3092535A US24927A US2492760A US3092535A US 3092535 A US3092535 A US 3092535A US 24927 A US24927 A US 24927A US 2492760 A US2492760 A US 2492760A US 3092535 A US3092535 A US 3092535A
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United States
Prior art keywords
liquor
pulp
cooking
magnesium
solution
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US24927A
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English (en)
Inventor
Ii George H Tomlinson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
HOWARD SMITH PAPER MILLS Ltd
SMITH PAPER MILLS Ltd HOWARD
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SMITH PAPER MILLS Ltd HOWARD
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Priority to US24927A priority Critical patent/US3092535A/en
Priority to GB13458/61A priority patent/GB987612A/en
Priority to DE1961S0073644 priority patent/DE1300822C2/de
Priority to AT319461A priority patent/AT249496B/de
Priority to FI0810/61A priority patent/FI40850B/fi
Priority to FR41508A priority patent/FR1287891A/fr
Application granted granted Critical
Publication of US3092535A publication Critical patent/US3092535A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • D21C3/22—Other features of pulping processes
    • D21C3/26—Multistage processes
    • D21C3/266—Multistage processes the same pulping agent being used in all stages

Definitions

  • the present -invention relates to Vthe manufacture of chemical pulps by a sulphite cooking process employing a relatively pure magnesium base cooking liquor having a relatively high total sulphur dioxide and essentially -free of excess sulphur dioxide, with an initial pH value in the range of 2.5-5.0.
  • the process involves impregnation of the wood chips under a substantial superatmospheric hydrostatic pressure, draining of surplus cooking liquor until a desired liquor-wood ratio is present, rapid heating of the chips to a high cooking temperature in the range of R-200 C., and regulating the discharge of SO2 formed from sulphurous acid generated during the cooking period to maintain the pH value of the cooking liquor in the range of 3 .tl-4.0, as lmeasured at room temperature, during the period in which the major sulphonation of the lignin and dissolution ofthe wood occurs.
  • the pulp residual liquor from this cooking method is of a character especially suitable for eiiicient recovery of its heat and chemical values in a cyclic recovery process, in which the residual liquor is separated yfrom the pulp, concentrated to a solids concentration of 50-70%, and the concentrated liquor burned in a chemical recovery unit with the recovery of heat, magnesium oxide and sulphur dioxide.
  • the ash obtained consists essentially of magnesium oxide, while the sulphur content is obtained in the form of sulphur dioxide at a concentration of about 1% in the gaseous products of combustion.
  • the magnesium bisulphite reagent is sufficiently mild in its action on cellulose that the increased concentration in the liquor required at this low liquor to wood ratio does not adversely affect strength or yield of pulp, and under certain conditions it may actually result in increased yield and greater strength.
  • This low liquor to wood ratio when employed, results in a reduced steam requirement for digestion, and also, because of the high solids content of the residual liquor under these conditions, a low steam requirement for subsequent evaporation of the residual liquor.
  • the process disclosed in said prior joint application when used for the production of pulp from wood chips comprises first displacing the air from pulp, with freedom from major odor problems.
  • the impregnated chips are then heated to a predetermined temperature in the range of 160-200" C.
  • This Velevated temperature is held for a predetermined period of time depending upon the temperature and pressure employed.
  • 160 C. this may be of the order of 3 to 4 hours, and at 190 C. may be as short as l() to 20 minutes, when the digester pressure is maintained about 5-15 p.s.i. above the vapor pressure of pure water at the digestion temperature, to give a chemical pulp having the desired quality and yield.
  • the digester pressure may then be lowered to atmospheric, and the lliquor washed from the pulp either before or after the pulp is removed from the digester.
  • the residual liquor thus obtained is evaporated to a solids concentration suitable for self-sustaining combustion and burned, a major portion of the liberated heat being converted to steam.
  • the magnesium oxide and sulphur dioxide formed on combustion of the liquor are subsequently recombined in aqueous solution to form fresh cooking liquor of the desired composition. rl ⁇ he make-up for losses in chemical is added either in the form of magnesium sulphate to the residual liquor before its combustion or as magnesium oxide to the fresh cooking liquor.
  • the process disclosed in said prior joint application combines the kraft pulping process versatility with regard to usable wood species with the magnesia base recovery process disclosed in Tomlinson U.S. Patent No. 2,385,955 to produce a high yield strong relatively bright unbleached
  • the magnesium base sulphite pulp although materially stronger than regular sulphite pulp, was found to be somewhat weaker than kraft pulp.
  • the main object of the present invention is the provision of an improved magnesium -base sulphite pulping process of the general character disclosed in said prior joint application which is capable of producing a sulphite chemical pulp materially stronger than regular sulphite pulp and approximately as strong as kraft pulp produced from similar wood chips.
  • the invention is concerned with a two-stage relatively pure magnesium base sulphite pulping process of the character described in which the first cooking stage follows the disclosure in said prior joint application as to pH value, pressure and temperature of the cookingliquor, and whenV about 30-45% of the Wood weight has been dissolved, continuously or intermittently injecting an aqueous suspension of magnesium hydroxide, Mg(OH)2, into the liquor while being circulated in the digester, to substantially increase the pH value of the liquor to a maximum value slightly on the acid side of neutrality, i.e. in the range of 6.0-6.5 pH, as measured at room temperature, and maintaining these conditions substantially throughout the second cooking stage.
  • the resulting pulp has been found to be substantially stronger than when the cooking is completed with the cooking liquor at a pH in the range of 3.0 to 4.0.
  • FIG. 1 is a schematic illustration of a pulp mill digester and chemical recovery system
  • Y FIG. 2 is a curve sheet showingrcomparative mag nesium base sulphite pulp cooking processes.
  • the digester 10 is substantially filled with wood chips, which may be any one of a wide variety of hardwoods or softwoods, or a mixture of several such Woods, in the usual manner and treated to promote subsequent penetration of the cooking liquor, for instance by presteaming at atmospheric pressure to displace air.
  • wood chips which may be any one of a wide variety of hardwoods or softwoods, or a mixture of several such Woods, in the usual manner and treated to promote subsequent penetration of the cooking liquor, for instance by presteaming at atmospheric pressure to displace air.
  • the magnesium bisulphite cooking liquor prepared as hereinafter described, and at a temperature about C. is then added until the digester is completely filled.
  • the liquor initially has a total SO2 content of about 4.0%, a combined SO2 content of 2.0% and a pH of 3.5.
  • the free SO2 will thus be 2.0% and there will be no excess sulphurous acid present.
  • the terms total SO2, free SO2, and combined SO2 are used herein as currently defined by the Technical Section, Canadian Pulp and Paper Association (Data Sheet C-OOc, lune 1955).
  • the pumping is continued until a digester hydrostatic pressure of about 90 p.s.i.g. is attained, to aid penetration of the chips.
  • the pH of the cooking ⁇ liquor tends to rise due to the transfer of SO2 from the liquid phase to the gas phase in the digester.
  • the pH increased from a value of 3.5 to a value of 4.25.
  • the volume of gas space in relation to the remaining liquor would be from the digester.
  • the total SO2 and the combined SO2 values also drop off rapidly as the SO2 is consumed in chemical reactions in the digesting process, as shown in solid lines in FlG. 2.
  • the later portion of the cooking process is formed by a second cooking stage in which the pH is increased to a Amaximum value slightly on the acid side of neutrality.
  • This has been found to give a stronger pulp in essentially the same yield, and for any degree of delignication, than -that obtained when the digestion is completed in the 3 to 4 pH range by the method described in said prior joint application.
  • This may be contrasted with bisulphite cooks using a soda xbase where pulping is completed in a second stage at alkaline pH and where such treatment results in considerable loss in yield compared with single stage bisulphite pulping.
  • magnesium hydroxide Mg(OH)2
  • Mg(OH)2 magnesium hydroxide
  • a suspension of magnesium hydroxide is injected into the cooking liquor while it is being circulated. This reacts with any excess sulphurous acid present to produce bisulphite and then with a portion of this bisulphite to produce magnesium sulphite. It simultaneously Vreacts with the acetic acid present to form magnesium acetate, thus increasing the pH as measured on a cooled sample withdrawn from the digester to a maximum value of about 6.5. The digestion is completed under these conditions.
  • the process set forth in said prior joint application operates with a cooking acid at a concentration of about 4% total SO2 and at a pH of about 2.5 to 5.0, this latter pH being essentially the upper limit because of the low solubility of magnesium sulphite which forms at high pH and the essentially complete insolubility of magnesium oxide and magnesium hydroxide.
  • the solubility of magnesium sulphite is 0.615% as magnesium sulphite or 0.38% as sulphur dioxide at 95 C., While that of magnesium hydroxide is only 0.000042% as magnesium hydroxide at 100 C. Thus it is impossible to impregnate the chips with sutiicient magnesium hydroxide and/or sulphite to carry out an alkaline cook.
  • the quantity of magnesium hydroxide added for the second stage cooking Iis preferably between 0.5 lb. and 4.0 lbs. (as magnesium oxide) per 100 lbs. of Wood chips. Quantities in excess of 4.0% of the wood quantity should not be used since they will result in deposition of magnesium sulphite crystals in the digester and Within kthe pulp.
  • the Mg(OH)2 addition should be made slowly to allow equilibrium between the higher pH liquor Vdiffusing into the chips and the more acidic liquor diffusing out. The dclignification reactions proceed more slowly as a result of the increased pI-l .obtained after injection and therefore a longer cooking time, land/ or a higher temperature should be used to complete the digestion.
  • the cooking liquor temperature was increased to about 175 C. and the pressure allowed to rise to about 130 p.s.i.g. Digestion was allowed to proceed for the same length of time and as indicated in broken lines, the total SO2 .and combined SO2 values vwere substantially higher at the end ofthe cook than in standard Magnete magnesium bisulpthite cooking.
  • the results of the softwood The kraft pulp could not be bleached to high brightness using the four-stage bleach procedure, and a sodium hypochlorite prebleach had to be used.
  • the two-stage pulps on the other hand, were readily chlorinated to a low permanganate number and bleached to 90 G.E. brightness or higher in the tourv stage procedure.
  • the described magnesium bisulphite pulpy cooking process is especially adapted to form part of a relatively simple and inexpensive cyclic system in which available heat and chemicals are effectively recovered from the digester residual liquor and the recovered chemicals recombined to form fresh cooking liquor for repeating the cycle.
  • the described cooking process is carried out in the digester 10, to which the wood chips and cooking acid are supplied in a well known manner.
  • the cooking liquor is circulated through and indi- -rectly heated in an external heat exchanger 12 by a pump 14.
  • a regulable supply line 16 for the magnesium hydroxide suspension is connected to the inlet side of the Ypump 14. This permits adjustment of the pH ofthe pletion of the two-stage cook through a blow tank 20 to the washers 18, from which the weak residual liquor is digester.
  • the concentrated liquor is sprayed into the upper end of a chemical 'recovery unit 24 along with combustion air and burned in suspension under self-sustaining combustion conditions in the furnace section thereof.
  • the fresh combustion gases with the M-gO ash particles in suspension and con- 'taining released SO2 are passed through the associated 'steam generating section 2.6 and air heater and economizer '28.
  • the suspended ash is separated in multi-cyclones 30 and passed to a retention tank 32, vacuum filter 34, and slaking tanks 36.
  • Make-up MgO is added to the system vat the tanks 36, mixed with water to form a suspension of Mg(OH)2, and delivered in part to the supply line 16.
  • magnesium oxide or hydroxide may beadded to the liquor following separation from the pulp at the washer to reduce Ythe disengagement of SO2 from solution during evaporation of the liquor.
  • the gaseous products of combustion and released SO2 are discharged by the induced draft fan 38 to a packed gas cooling tower 40, in which the ascending gas is contacted with a descending flow of recycled cooled liquor to which a portion of the Mg(OH)2 slurry from tank 36 is added, which results in a partial absorption ot SO2 from the gas.
  • the gases leaving the upper end of the cooling tower 40 pass through Ya Venturi gas scrubber 42, collec tion tank 44, a second Venturi gas scrubber 46, and nally through a cyclone separator 48 to the stack.
  • the gases are contacted with a spray of recycled liquor, to which controlled amounts of Mg(OH)2 have been added, for absorption of additional SO2 from the gases.
  • the liquor droplets in suspension are separated from the gas stream by the change of direction and low velocity in the tanks 44 and 48. Liquor from the primary absorption system leaves collection tank 44 and goes to acid storage tank 5S where the liquor is recycled through a Venturi scrubber 56.
  • the liquor leaving the primary absorption system will contain magnesium bisulphite and a small amount of magnesium monosulphite.
  • the composition of the l-iquor recycling from tank '58 may be controlled to give theiinal adjustment of liquor composition, i.e. Ito provide a solution having a chemical composition corresponding approximately to the formula Mg (H503 s
  • the additionalmake-up SOzrequired to keep the system in balance goes directly Ito the duct carrying the combustion gases to the cooling tower 40 and mixes therewith.
  • the primary purpose of the cooling tower 40 is to cool the hot furnace ue gas to a temperature of about 40 C.
  • the cooking acid is withdrawn from the strong acid storage tank 58 as needed in -the digester-IG.
  • the cooking acid is readily maintained in the tank at the desired temperature and essentially free yof excess sulphurous acid.
  • the total SO2 may be 5.04%, combined SO2 2.52 and free SO2 2.52.
  • the method of preparing a chemical pulp from cellulosic raw material comprising impregnating the material with a magnesium bisulphite solution essentially free of excess sulphurous acid and initially in the range 2.5-5.0 pH, digesting the cellulosic material at a temperature between 160 and 200 C., for a predetermined digestion period while maintaining the pH of the solution as measured at room temperature at a value between 3.0 and 4.0 during the period when the major sulphonation of the l-ignin and dissolution from the cellulose takes place, and increasing the pH of the solution to -a maximum value in the range of 4.75-6.5 las measured at room temperature during the nal portion of the digestion period by the addition of an alkaline magnesium compound to the solution to form a deiibred pulp without mechanical refining.
  • the cooking temperature is maintained in the range between and 200 C.
  • the pH value of the solution las measured at room temperature is maintained at a value between 3.0 and 4.0 during the period when the major sulphonation of the lignin and disso'lution from the wood takes place, and maintaining the pH of the solution as measured at room temperature in the range 'of 6.0 ⁇ and 6.5 during the final portion of the digestion period by the addition of an alkaline magnesium compound rto the solution to form a deibred pulp without mechanical refining.
  • the method of preparing a chemical pulp from cellulosic raw material comprising impregnating the material with -a magnesium bisulphite solution essentially free of excess sulphurous acid and initially in the range ⁇ 2.5-5.0 pH, digesting the cellulosic material at a temperature between 160 and 200 C., for a predetermined digestion period varying between approximately ten minutes and four hours, the lower the digestingtemperature -the longer the digestion time and vice versa, while maintaining the pH of the solution during a major portion of the digestion period between 3.0 and 4.0 as measured at room temperature, and during Ithe nal portion of the digestion period increasing the pH to a maximum value in the range of 4.75-6.5 as measured 'at room temperature by the addition of magnesium hydroxide to the solution, to form a deiiored pulp without mechanicai reiining.
  • the method of preparing a chemical pulp from cellulosic raw material comprising impregnating the material with a magnesium bisulphite solution essentially free of excess sulphurous acid and initially in the range 3.5-5.0 pH, and digesting the cellulosic material at a temperature between 160 and 200 C., for a predetermined digestion period while maintaining the piti or" the solution during a major portion of the digestion period between 3.0 and 4.0 as measured at room temperature by regulating the digesting pressure to retain sulphurous acid iiberated during the digestion, maintaining the pH of the solution as measured at room temperature in the range of 6.0 and 6.5 by the addition of magnesium hydroxide to the solution lduring the iinal portion of the digestion period, and increasing the digesting temperature during the period in which the increased pH is maintained, to form a deiibred pulp without mechanical reiining.
  • a cyclic process of preparing a chemical pulp from a cellulosic raw material which comprises impregnating the material with a cooking liquor consisting of a magnesium bisulphite solution essentially free of excess sulphurous acid and having a pH of 2.5 to 5.0, rapidly heating the material to a cooking temperature in the range of 160-200 C., holding the digester at said cooking temperature for a predetermined period While maintaining the pH of the solution as measured at room temperature at a value between 3.0 and 4.0 during the period when the major sulphonation of the lignin and dissolution from the cellulose takes place7 increasing the pH of the solution in the digester to a maximum value in the range oi 4.75-6.5 as measured at room temperature during the final portion of the digestion period by the addition of an alkaline magnesium compound to the solution, separating the residual liquor from the pulp, concentrating the residual liquor to a predetermined solids concentration suitable for self-sustaining combustion, burning the concentrated liquor with the production of heat, magnesium oxide and gaseous products including sulphur dioxide
  • a cyclic process of preparing a chemical pulp from a cellulosic raw material which comprises steaming chips of the cellulosic material in a digester to displace air

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US24927A 1960-04-27 1960-04-27 Sulphite pulping process Expired - Lifetime US3092535A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
US24927A US3092535A (en) 1960-04-27 1960-04-27 Sulphite pulping process
GB13458/61A GB987612A (en) 1960-04-27 1961-04-14 Sulphite pulping process
DE1961S0073644 DE1300822C2 (de) 1960-04-27 1961-04-24 Verfahren zur gewinnung von zellstoff
AT319461A AT249496B (de) 1960-04-27 1961-04-24 Verfahren zur Herstellung von Zellstoff
FI0810/61A FI40850B (sv) 1960-04-27 1961-04-25
FR41508A FR1287891A (fr) 1960-04-27 1961-04-27 Procédé de réduction en pulpe par sulfite

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US24927A US3092535A (en) 1960-04-27 1960-04-27 Sulphite pulping process

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AT (1) AT249496B (sv)
DE (1) DE1300822C2 (sv)
FI (1) FI40850B (sv)
FR (1) FR1287891A (sv)
GB (1) GB987612A (sv)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3844879A (en) * 1972-10-30 1974-10-29 Babcock & Wilcox Co System for removing sodium chloride contaminants from a magnesium base pulping process
US4929307A (en) * 1985-11-29 1990-05-29 A. Ahlstrom Corporation Method of decreasing black liquor viscosity
US4963231A (en) * 1988-06-13 1990-10-16 Ahlstromforetagen Svenska Ab Method for evaporation of liquids
CN114851332A (zh) * 2022-05-31 2022-08-05 东北林业大学 一种具有磁各向异性的木质机器人制备方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1864620A (en) * 1931-02-18 1932-06-28 Brown Co Process of liberating pulp from raw cellulosic materials
US2019598A (en) * 1932-03-04 1935-11-05 Dreyfus Henry Production of cellulosic materials or cellulose
US2118074A (en) * 1935-07-10 1938-05-24 Dreyfus Henry Manufacture of cellulose
US2385955A (en) * 1941-04-08 1945-10-02 George H Tomlinson Manufacture of sulphite pulp
US2749241A (en) * 1949-07-12 1956-06-05 Dev Tecnique De La Pate A Papi Process for producing semi-chemical pulp

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2730445A (en) * 1952-03-21 1956-01-10 Sivola George Integrated lignocellulose digestion and recovery process
US3046182A (en) * 1956-01-13 1962-07-24 Smith Paper Mills Ltd Howard Sulphite pulping process

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1864620A (en) * 1931-02-18 1932-06-28 Brown Co Process of liberating pulp from raw cellulosic materials
US2019598A (en) * 1932-03-04 1935-11-05 Dreyfus Henry Production of cellulosic materials or cellulose
US2118074A (en) * 1935-07-10 1938-05-24 Dreyfus Henry Manufacture of cellulose
US2385955A (en) * 1941-04-08 1945-10-02 George H Tomlinson Manufacture of sulphite pulp
US2749241A (en) * 1949-07-12 1956-06-05 Dev Tecnique De La Pate A Papi Process for producing semi-chemical pulp

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3844879A (en) * 1972-10-30 1974-10-29 Babcock & Wilcox Co System for removing sodium chloride contaminants from a magnesium base pulping process
US4929307A (en) * 1985-11-29 1990-05-29 A. Ahlstrom Corporation Method of decreasing black liquor viscosity
US4963231A (en) * 1988-06-13 1990-10-16 Ahlstromforetagen Svenska Ab Method for evaporation of liquids
CN114851332A (zh) * 2022-05-31 2022-08-05 东北林业大学 一种具有磁各向异性的木质机器人制备方法
CN114851332B (zh) * 2022-05-31 2023-02-17 东北林业大学 一种具有磁各向异性的木质机器人制备方法

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FR1287891A (fr) 1962-03-16
DE1300822C2 (de) 1975-01-09
GB987612A (en) 1965-03-31
FI40850B (sv) 1969-02-28
DE1300822B (de) 1975-01-09
AT249496B (de) 1966-09-26

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