US3216887A - Preparation of sulfate pulping liquor with polysulfide - Google Patents

Preparation of sulfate pulping liquor with polysulfide Download PDF

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Publication number
US3216887A
US3216887A US368365A US36836564A US3216887A US 3216887 A US3216887 A US 3216887A US 368365 A US368365 A US 368365A US 36836564 A US36836564 A US 36836564A US 3216887 A US3216887 A US 3216887A
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liquor
content
mixture
polysulfide
black liquor
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Landmark Per Andreas
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PAPIRIND FORSKNINGSINST
PAPIRINDUSTRIENS FORSKNINGSINSTITUTT
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PAPIRIND FORSKNINGSINST
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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
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/0057—Oxidation of liquors, e.g. in order to reduce the losses of sulfur compounds, followed by evaporation or combustion if the liquor in question is a black liquor

Definitions

  • This invention relates to a method for preparing a cooking liquor with a high content of polysulphide to be used in the sulphate wood pulping process.
  • the high content of polysulphide is intended to increase the pulp yield and to prevent corrosion of the digesters.
  • the eiiective alkali in the liquor is defined as the sum of the content of sodium hydroxide and half of the content of sodium sulphide calculated as sodium hydroxide (NaOH+ /2Na S).
  • the sulphidity of the liquor is defined as the ratio between the content of sodium sulphide and the sum of sodium hydroxide and sodium sulphide, calculated as Na-equivalents Nags
  • the content of polysulphide in the cooking liquor is also of importance for the corrosion of the digester. Corrosion of sulphate digesters made of mild steel plates is caused by the polysulphide in the cooking liquor, this chemical acting as a cathodic depolarizor.
  • the rate of corrosion increases with increasing concentrations of Na S NaOI-I, Na s and Na S O in the cooking liquor, while increasing content of Na SO will reduce the rate of corrosion.
  • corrosion is critical only during the first stage of the cooking period. The metal later becomes passive, whereby further attack on the metal is prevented. This has been established by weight loss experiments (L. Stockman and L. Ruus, Vvensk Papperstidning 57, 831 (1954)), and by electrochemical measurements carried out by use of a specially developed Ag/AgS electrode.
  • the tendency of the steel plates to become passive is strongly influenced by the composition of the cooking liquor, but not in the same way as the rate of corrosion of the active steel plates. While the rate of corrosion increases With increasing amounts of polysulphide when the content of the same is low, a high content of polysulphide will induce passivation.
  • a polysulphide enriched cooking liquor can be prepared by adding alkali polysulphide to the cooking liquor. This method is disclosed in the cited US. Patent No. 2,944,928. As prior known, polysulphide enriched cooking liquor can also be prepared by dissolving elemental sulphur in an aqueous sodium hydroxide or sulphide solution. Said method is used, for example, by Peckham and May: TAPPI (January 1960), No. 1: 45. However, the use of cooking liquors prepared according to these methods give undesirable effects in the liquor recovery system.
  • the polysulphide added will after digesting and the subsequent combustion of the black liquor occur as sulphide and in amounts eX- ceeding the normal sulphur losses in the process.
  • This causes a continuous increase in the sulphidity of the cooking liquor, resulting in an increased risk of a more poorly digested pulp, and an increased corrosion in the recovery system as well as increased contamination. This is well known in the field, and efforts have been made for eliminating these obstacles.
  • the process which will be described in the following significantly reduces these difficulties.
  • the present invention is based upon the fact that by oxidation of a mixture of black liquor and white liquor the lignin dissolved in the black liquor, the sulphate llgnin, will cause formation of considerable amounts of polysulphide together with thiosulphate, and the oxidation also proceeds faster.
  • W. A. Mueller (Pulp and Paper Magazine of Canada 66T3 (1959)) points out that the tendency of passivation o of the digester plates increases when the digesters are charged with oxidized black liquor.
  • W. A. Mueller then refers to a black liquor which is oxidized under conditions which aim at the conversion of Na S to Na S O Said oxidation is carried out in a number of sulphate mills, primarily in order to reduce evaporator corrosion.
  • the process according to the present invention is based on the discovery that when the mixture of black liquor and white liquor, which is charged to the digester, is partially oxidized with air in a suitable equipment, polysulphide is formed, which in turn increases the pulp yield and passivates the steel plates of the digesters.
  • Said oxidation process differs significantly from the conventional oxidation of black liquor in that the latter aims at a complete conversion of Na S into Na S O whereas the present invention prescribes a partial conversion of Na s to Na s in a mixture of black liquor and white liquor, while further oxidation to Na S O is mainly avoided.
  • Polysulphide concentration high enough always to secure passivation of the plates cannot be obtained by oxidation of black liquor alone.
  • the said partially oxidized mixture is a new product which is fundamentally different from the industrial produced called oxidized black liquor.
  • black liquor black liquor To the white liquor black liquor is added. Nonevaporated black liquor (raw liquor), partly evaporated black liquor (weak liquor), or evaporated black liquor (strong liquor) can be used.
  • the black liquor content of the mixture can vary between and 80%.
  • the mixture is oxidized with air in a suitable equipment. Air of atmospheric pressure or compressed air can be used. During the oxidation the sodium sul phide content of the liquor will decrease and the polysulphide content will increase to a maximum. By further oxidation the polysulphide content will again decrease and the initial sulphide content will finally be totally converted into thiosulphate. The oxidation must, therefore, be interrupted at a time when the polysulphide content reaches its highest value. This will usually occur when 1435 g. Na S/l. is oxidized. The required amount of air for such an oxidation is by complete utilization of the air oxygen about 20-50 times the liquor volume.
  • the digester is charged with the oxidized mixture of white and black liquor and the liquor to wood ratio is regulated by addition of small amounts of black liquor.
  • the digestion is carried out in the usual way and the chemicals are recovered as described for the conventional sulphate process.
  • the sulphur losses will be higher than normal during the recovery process.
  • the increased sulphur losses can, therefore, best becompensated by addition of elemental sulphur which. is dissolved in the cooking liquor.
  • the oxidation was carried out in an apparatus at 70 C. as shown in FIG. 1 (agitated gas-liquid contactor).
  • the rate of air was determined by means of a rotameter.
  • the air was supplied to the bottom of the tank and was distributed in the liquor by means of a rotating agitator and baffles inserted in the walls of the tank. Foam was depressed by means of fan blades mounted on the agitators axis.
  • the spent gas is led through an instrument for measurement of the residual oxygen content.
  • the composition of the liquor before the oxidation was:
  • the air was fed into the apparatus below the sieve bottom.
  • the air was preheated to about 70 C. and saturated with water vapor before it entered the sieve bottom.
  • the total hole area of the sieve bottom was 3.3% of the total area and the diameter of the holes'was 2.5 mm.
  • composition of the liquor before the oxidation was:
  • Ratio white liquorzblack liquor 1.6:1 Effective alkali g./l 70 Na S g./l 46 Nazszog g./1 Na s (calculated as Na S g./l 2 Liquor volume in the apparatus 11.5 Rate of air flow 1./s 16 Oxidation time mins 5 Ratiod airzliquor 320021
  • the composition of the oxidized liquor was:
  • the yield of pulp (on wood) was at Kappa No. 35, 3.4% higher than by conventional sulphate digestion and 2.4% higher than from digesting experiments with nonoxidized cooking liquor to which 1% S (on wood) was added, under less equal cooking conditions.
  • a process for the preparation of a cooking liquor of high polysulfide content, the steps comprising, digesting cellulose material in a sulfate pulping process, thereafter separating the spent, black liquor from the digested material, said black liquor containing dissolved sulfate lignin, subsequently mixing of from 5 to percent by volume of black liquor with from 20 to percent by volume of white liquor, said white liquor, having a sulfidity of from 40 to percent, thereafter partially oxidizing the mixture with oxygen with a consumption of from 1.4 to 14 cubic meters of oxygen per cubic meter of said mixture, said dissolved sulfate lignin promoting the formation of polysulfide, whereby the sodium sulfide content of the mixture will be decreased and the polysulfide content of the mixture will be increased.
  • said black liquor being non-evaporated raw black liquor.
  • the amount of polysulfide, calculated as Na S of the mixture prior to oxidation being about 2 grams per liter, and after the oxidation being about grams per liter.

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US368365A 1961-05-27 1964-05-18 Preparation of sulfate pulping liquor with polysulfide Expired - Lifetime US3216887A (en)

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Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3470061A (en) * 1967-03-03 1969-09-30 Union Camp Corp Sodium polysulfide pulping process and regeneration
US3617431A (en) * 1966-03-03 1971-11-02 Mo Och Domsjoe Ab Process for preparing cellulose pulp by alkaline digestion while inhibiting extraction of hemicellulose
US3860479A (en) * 1971-06-18 1975-01-14 Union Camp Corp Catalytic oxidation of alkaline pulping liquor
US3874991A (en) * 1968-08-23 1975-04-01 Westvaco Corp Polysulfide impregnation of lignocellulosic materials in a continuous digester
US4153502A (en) * 1977-05-06 1979-05-08 Corrosion Service Company Limited Process for the production of polysulphide pulping liquor from pulp mill recovery smelt
US4162187A (en) * 1974-05-09 1979-07-24 The Mead Corporation Process for production of sodium thiosulfate and sodium hydroxide
US4242177A (en) * 1976-04-07 1980-12-30 Mitsubishi Paper Mills, Ltd. Method for oxidizing malodorous sulfur compounds in kraft cooking liquor
WO1983001469A1 (en) * 1981-10-21 1983-04-28 Nils V Mannbro A method of polysulphide treatment in alkaline pulping of lignocellulose material
US4507172A (en) * 1982-09-16 1985-03-26 St. Regis Paper Company Kraft pulping process
US4855123A (en) * 1986-04-18 1989-08-08 Mitsubishi Paper Mills, Ltd. Method of oxidizing sulfide-containing liquor
US5082526A (en) * 1989-01-23 1992-01-21 Pulp And Paper Research Institute Of Canada Process of producing kraft pulping liquor by the oxidation of white liquor in the presence of lime mud
EP1245721A1 (en) 1999-06-15 2002-10-02 Kawasaki Kasei Chemicals Ltd. Digestion method for pulp
US20060094920A1 (en) * 2004-10-29 2006-05-04 Roper Ralph E Jr Calcium-sodium polysulfide chemical reagent and production methods
US20140024093A1 (en) * 2012-03-29 2014-01-23 Shell Oil Company Process for the production of digested biomass useful for chemicals and biofuels

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2481408A (en) * 1946-08-13 1949-09-06 Olin Mathieson Regeneration of caustic soda-sodium sulfide cooking liquor
US2944928A (en) * 1957-09-20 1960-07-12 Kibrick Method of preparing paper pulp

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2481408A (en) * 1946-08-13 1949-09-06 Olin Mathieson Regeneration of caustic soda-sodium sulfide cooking liquor
US2944928A (en) * 1957-09-20 1960-07-12 Kibrick Method of preparing paper pulp

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3617431A (en) * 1966-03-03 1971-11-02 Mo Och Domsjoe Ab Process for preparing cellulose pulp by alkaline digestion while inhibiting extraction of hemicellulose
US3470061A (en) * 1967-03-03 1969-09-30 Union Camp Corp Sodium polysulfide pulping process and regeneration
US3874991A (en) * 1968-08-23 1975-04-01 Westvaco Corp Polysulfide impregnation of lignocellulosic materials in a continuous digester
US3860479A (en) * 1971-06-18 1975-01-14 Union Camp Corp Catalytic oxidation of alkaline pulping liquor
US4162187A (en) * 1974-05-09 1979-07-24 The Mead Corporation Process for production of sodium thiosulfate and sodium hydroxide
US4242177A (en) * 1976-04-07 1980-12-30 Mitsubishi Paper Mills, Ltd. Method for oxidizing malodorous sulfur compounds in kraft cooking liquor
US4153502A (en) * 1977-05-06 1979-05-08 Corrosion Service Company Limited Process for the production of polysulphide pulping liquor from pulp mill recovery smelt
WO1983001469A1 (en) * 1981-10-21 1983-04-28 Nils V Mannbro A method of polysulphide treatment in alkaline pulping of lignocellulose material
US4507172A (en) * 1982-09-16 1985-03-26 St. Regis Paper Company Kraft pulping process
US4855123A (en) * 1986-04-18 1989-08-08 Mitsubishi Paper Mills, Ltd. Method of oxidizing sulfide-containing liquor
US5082526A (en) * 1989-01-23 1992-01-21 Pulp And Paper Research Institute Of Canada Process of producing kraft pulping liquor by the oxidation of white liquor in the presence of lime mud
EP1245721A1 (en) 1999-06-15 2002-10-02 Kawasaki Kasei Chemicals Ltd. Digestion method for pulp
US20060094920A1 (en) * 2004-10-29 2006-05-04 Roper Ralph E Jr Calcium-sodium polysulfide chemical reagent and production methods
US7534413B2 (en) 2004-10-29 2009-05-19 Heritage Environment Services, Llc Calcium-sodium polysulfide chemical reagent and production methods
US20140024093A1 (en) * 2012-03-29 2014-01-23 Shell Oil Company Process for the production of digested biomass useful for chemicals and biofuels

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