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US3619349A - Bleaching of shredded or fluffed cellulosic pulp with gaseous chlorine monoxide - Google Patents

Bleaching of shredded or fluffed cellulosic pulp with gaseous chlorine monoxide Download PDF

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Publication number
US3619349A
US3619349A US882819A US3619349DA US3619349A US 3619349 A US3619349 A US 3619349A US 882819 A US882819 A US 882819A US 3619349D A US3619349D A US 3619349DA US 3619349 A US3619349 A US 3619349A
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United States
Prior art keywords
pulp
percent
chlorine
consistency
chlorine monoxide
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Expired - Lifetime
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US882819A
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English (en)
Inventor
Norman Liebergott
Henry Irving Bolker
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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
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
    • D21C9/123—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with Cl2O

Definitions

  • the present invention relates to the bleaching of cellulosic pulp and in particular relates to the bleaching of cellulosic pulp at high consistency in fluffed or shredded from, with gaseous chlorine monoxide.
  • the multistage bleaching of an unbleached chemical cellulosic, e.g. wood, pulp, the pulp from the digestion stage in for example the kraft, soda or sulfite process, normally after washing, is treated to render at least a portion of the ligneous impurities readily soluble in water, whilst, of the ligneous impurities not readily soluble in water, at least a portion is readily soluble in a dilute aqueous alkali such as dilute aqueous solutions of sodium hydroxide, sodium sulfite or ammonium hydroxide.
  • a dilute aqueous alkali such as dilute aqueous solutions of sodium hydroxide, sodium sulfite or ammonium hydroxide.
  • the pulp is conventionally treated with agents such as chlorine, chlorine dioxide or the oxides of nitrogen, more usually chlorine or chlorine dioxide or mixtures thereof.
  • the aforesaid pretreated" pulp after washing with water is subjected to caustic extraction with for example sodium hydroxide to remove the water insoluble ligneous impurities therefrom, this extraction being generally conducted on the pulp at low consistency in the range to 14 percent, a temperature in the range 40 to 70 C. and at a retention time of 60 to 120 minutes.
  • the extracted pulp is oxidized with chlorine dioxide generally at a low consistency of from 6 to l5 percent, at a temperature of from 60 to 75 C. for a retention time of 3 to 5 hours.
  • the aforesaid three stages are present in all multistage bleaching processes for chemical cellulosic pulps although variations are possible with regard to the stages.
  • pulps made from certain wood species treatment with sodium or calcium hypochlorite may be desirable between the extraction with for example sodium hydroxide and the chlorine dioxide oxidative treatment.
  • the chlorine dioxide treatment is normally repeated a caustic extraction stage being interposed between the two chlorine dioxide oxidation stages.
  • the treatment of the pulp is carried out in slurry form at low consistencies varying from 3 to 15 percent, at temperatures ranging from ambient to about 75 C. and for retention times from about 30 minutes to about 5 hours.
  • fluffed chemical cellulosic pulp (sometimes referred to as shredded chemical cellulosic pulp) is the product obtained by the fragmentation of a chemical cellulosic pulp into fibers and fiber aggregates or flocks, substantially each discrete fiber aggregate or flock being spongy compressible and readily gas permeable.
  • Each of said fiber aggregates or flock is usually an average of an eighth to 1 inch in diameter and prevents a flutfed up dry appearance even with about 70 to 80 percent moisture in the cellulosic pulp.
  • fluffing or shredding of chemical cellulosic pulp is directed to a process of producing this pulp by fragmentation. in particular, in Canadian Pat.
  • a process for bleaching of a fibrous cellulosic pulp particularly a chemical cellulosic pulp which comprises contacting the pulp at a high consistency and in the form of flulTed or shredded fibers and fiber aggregates with chlorine monoxide in the gaseous phase.
  • chlorine monoxide in the bleaching of chemical cellulosic fibrous pulps in the gaseous phase at high consistency and in fluffed and shredded form, chlorine monoxide can be used with advantage in those stages where chlorine dioxide is hitherfore been used.
  • chlorine monoxide to achieve a similar oxidative bleaching efiect on chemical cellulosic pulp with chlorine dioxide, the period of contact between the chlorine monoxide gas and the pulp to achieve a similar pulp brightness is substantially reduced yielding an even greater cost saving in the bleaching of the pulp and inter alia and more precise control over the bleaching operation and a further saving in bleaching chemicals.
  • a process for bleaching of a chemical cellulosic pulp, particularly wood pulp which comprises contacting the pulp at a high consistency and in the form of fluffed or shredded fibers or fiber aggregates with chlorine monoxide in the gaseous phase.
  • the pulp on contact with the gaseous chlorine monoxide is a high consistency pulp, suitably having a consistency of at least percent, preferably a consistency in the range 15 to 50 percent and more desirably in the range l5 to percent, at which consistency it is shredded and fluffed particularly by the method set forth in Canadian Application 988,372 into fibers and fiber aggregates.
  • a consistency pulp suitably having a consistency of at least percent, preferably a consistency in the range 15 to 50 percent and more desirably in the range l5 to percent, at which consistency it is shredded and fluffed particularly by the method set forth in Canadian Application 988,372 into fibers and fiber aggregates.
  • the chlorine monoxide gas should be diluted with a nonreactive gas such as air, carbon dioxide or nitrogen to a partial pressure not greater than about one-third of an atmosphere, i.e. about 253 mm. of mercury. This is in contrast to chlorine dioxide gas which must be diluted with a nonreactive gas to a much lower partial pressure of not greater than [00 mm. of mercury to avoid the risk of explosion.
  • the process of the present invention may be operated at a high partial pressure of chlorine monoxide suitably above 100 mm.
  • the temperature of reaction between the gaseous chlorine monoxide and the pulp is not particularly critical and is desirably in the range from 30 C. to 50 C. It has been found that chlorine monoxide bleaching of pulp according to the present invention produces an exothermic reaction. 1f the partial pressure of chlorine monoxide is above I00 mm. of mercury, and the consistency of the flufied pulp is in the range of 25 to percent. the temperature of the mixture is found to rise from 23 C. to 46 C. Thus when operating with a high concentration of chlorine monoxide at a high pulp consistency, no external heat is necessary for the bleaching process. When the partial pressure of the chlorine monoxide is below 100 mm. of mercury and especially in the range of from l to 20 mm. of mercury, it is beneficial to heat the mixture to about C. and to maintain the temperature during the reaction or retention period.
  • the pH of the pulp maintained in the process of the present invention has a substantial effect in the brightness of the pulp obtained and on the viscosity of the pulp obtained.
  • the highest brightness values are achieved at pHs in the range of from about 5.5 to about 8 but at the same time the viscosity of the pulp falls markedly in this pH range.
  • the high brightness-low viscosity pulp produced in the aforementioned pH range has certain end uses when bleaching pulp for use in the paper industry wherein pulp with 0.5 percent CED viscosity below about 15 is not useful, it is preferred to operate below 5.5 and suitably in the range 3.5 and 5.5 i.e. in the acid range or alternatively above 8 and suitably in the range 8 to l l, i.e.
  • the pH of the reaction mixture may be controlled by adding a buffering agent, such as an alkali metal salt of a weak acid, e.g. sodium carbonate, to the pulp before contact with the gaseous chlorine monoxide.
  • a buffering agent such as an alkali metal salt of a weak acid, e.g. sodium carbonate
  • ammonia or compounds of ammonia such as sulfamic acid in small amounts (l-3 percent) to the pulp before contact with the gaseous chlorine monoxide and suitably prior to the fluffing and shredding of the pulp protects the pulp against excessive lowering of the viscosity thereof during the process.
  • This aspect of the invention has particular application when operating at high partial pressures of chlorine monoxide suitably in the range to 200 mm. of mercury and at higher temperatures in the range 45 to 50 C. when the viscosity of the product pulp obtained is lowest. It has been found that small amounts of chlorine dioxide e.g.
  • FIG. 1 is a graph showing the variation of the brightness of the pulp produced according to the present invention with PH and FIG. 2 is a graph showing the variation in 0.5 percent CED viscosity of the pulp produced according to the present invention with pH.
  • EXAMPLE 1 (a) An unbleached sulfite pulp from coniferous wood having a Roe chlorine number of 7.9, a CED viscosity of 35.6 c.p.s. and a Kappa number of 33.0, was chlorinated, extracted with dilute sodium hydroxide and washed with water. The pretreated, i.e. partially delignified pulp had a Kappa number of 1.0, a CED viscosity of 33.l c.p.s., and a Elrepho brightness of 57.7 percent.
  • a portion of the pretreated pulp was pressed to 35 percent consistency and the pressed pulp was sprayed with a solution containing sodium carbonate equal to l percent by weight of the pulp and water sufiicient to reduce the consistency to 30 percent, i.e. to a moisture content of 70 percent.
  • the pulp was then shredded into fiber and fiber ag gregates, by the method set forth in Canadian Pat. application 988,372 and the fluffed pulp was placed in a tower at room temperature. Chlorine monoxide diluted with air to a partial pressure of 210 mm. of mercury was passed into the tower until 0.6 percent chlorine monoxide based on oven-dry pulp was added to the pulp.
  • the reaction temperature rose from 23 C. to 46 C. within 1 minute reaction time.
  • the final pH of the pulp was 4.6.
  • the bleached pulp was washed, air-dried and the brightness and CED viscosity measured.
  • the brightness was 91.8 percent on the Elrepho meter and the pulp had a 0.5 percent CED viscosity of 14.9 c.p.s.
  • Chlorine monoxide is a well-known gas and may be prepared for example by the methods disclosed in U.S. Pat. Nos. 2,155,281; 2,157,524; 2,157,525; and 2,157,559.
  • EXAMPLE 2 In a similar manner as in example 1(a) a series of pulps the same as in example 1(a) were treated at 30 percent consistency and at a partial pressure of 210 mm. of mercury with gaseous chlorine monoxide diluted with air until from 0.61 to 0.66 percent chlorine based on oven dry pulp was added to the pulp. The period of time in one series of pulps was 60 minutes, the results being given in table 1 and in a second series of pulps l minute the results being given in table 11. The temperature during the process rose from 23 to 46 C.
  • a pulp of a desired brightness and desired viscosity can be obtained by adjusting the pH of the mixture.
  • the pH may be adjusted to range between 3.5 and 5.5 or from 8 to 11.
  • a pH range from 5.5 to 8 may be employed.
  • EXAMPLE 3 An unbleached kraft pulp from coniferous wood having a Roe chlorine number of 4.6, a Kappa number of 26.8 and a CED viscosity of 29.2 cps. was chlorinated, extracted with dilute sodium hydroxide and washed with water.
  • the pretreated, i.e. partially delignified pulp had a Kappa number of 7.3, a CED viscosity of 28.6 cps. and an Elrepho brightness of 31.6 percent.
  • the pretreated pulp was pressed to 35 percent consistency and three different portions of this pulp were sprayed respectively with a solution containing 1, 2 or 3 percent sodium carbonate on pulp and water to bring the consistency of each portion to 30 percent.
  • the three portions were then shredded or fluffed into fiber and fiber aggregates in a similar manner as in example 1 and each portion was placed in a tower maintained at 40 C. in a heating bath. Chlorine monoxide diluted to a partial pressure of 5 mm. of mercury was passed into each tower until 1.25 percent chlorine monoxide based on oven dry pulp was added to each portion the re tention time in each case being 5 minutes. The final pH of each portion of the pulp. the brightness and the viscosity of the pulps after washing and air drying are set out in the table below.
  • sulfamic acid is premixed with the pulp prior to the addition of the chlorine monoxide
  • One portion of the pretreated pulp was pressed to 30 percent consistency and then shredded into fiber and fiber aggregates. Chlorine monoxide, diluted with air to a partial pressure of 210 mm. of mercury, was passed into the tower until 0.6 percent chlorine monoxide, based on oven dry pulp, was added to the pulp. The reaction temperature rose from 23 C. to 46 C. in 1 minute reaction time. The final pH of the pulp was 3.0. The bleached pulp was washed, air-dried and the final brightness and CED viscosity measured. The brightness was 88.1 on the Elrepho meter and the pulp had a 0.5 percent CED viscosity of 19.0 cps.
  • the brightness was 87.3 percent on the Elrepho meter and the pulp had a 0.5 CED viscosity of 23.8 cps. Under similar conditions with the final pH 4.5 the Elrepho brightness was 91.3 percent and the 0.5 percent CED viscosity was 21.3 cps. in the product pulp.
  • EXAMPLE 5 This example compares the efiect of chlorine-monoxide and chlorine dioxide on chlorinated and extracted (pretreated) sulfite pulp, percent consistency at a temperature: of 27 C.
  • a portion of the chlorinated and extracted pulp from example 4 was pressed to percent consistency and sprayed with a solution containing sodium carbonate equal to 1 percent by weight of the pulp and water sufficient to reduce: the consistency to 15 percent. i.e. a moisture content of 85 percent.
  • the pulp was then shredded into fiber and fiber aggregates.
  • (a) An aliquot of the above pulp was placed in a tower at room temperature 23 C. Chlorine monoxide diluted to a partial pressure of 53 mm. of mercury was added to the pulp. The reaction temperature rose to 27 C. within 1 minute reaction time. The final pH of the pulp was 5.0. The bleached pulp was washed, air-dried and the brightness and CED viscosity measured. The brightness was 90.4 percent on the Elrepho meter and the pulp had a 0.5 percent CED viscosity of 24.8.
  • EXAMPLE 6 This example demonstrates the use of ammonia as the extractant in the alkali extraction stage in the pretreated pulp, rather than caustic soda, and how it helps to protect the viscosity in the chlorine monoxide bleaching stage. The example can be compared to example 4(a).
  • the unbleached sulfite pulp having a Roe number of 7.9 and CED viscosity of 35.6 and a Kappa number of 33, was chlorinated and extracted with an ammonia/steam gaseous mixture, by the method set forth in Canadian Pat. application 752,864.
  • the pretreated, i.e. partially delignified pulp had a Kappa number of 1.3, a CED viscosity of 32.8 and an Elrepho brightness of 56.1 percent.
  • a portion of the pretreated pulp was pressed to 20 percent consistency and the pressed pulp was sprayed with a solution containing sodium carbonate equal to 1 percent by weight of the pulp and water sufficient to reduce the consistency to 15 percent, i.e. moisture content of percent.
  • the pulp was then shredded into fiber and fiber aggregates, and the fluffed pulp was placed in a tower at room temperature. Chlorine monoxide, diluted with air to a partial pressure of 53 mm. of mercury, was passed into the tower until 0.6 percent chlorine monoxide based on oven-dry pulp was added to the pulp. The reaction temperature rose from 23 C. to 25 C. The final pH of the pulp was 5.2. The bleached pulp was washed, air-dried and the brightness and CED viscosity measured. The brightness was 88.4 percent on the Elrepho meter and the pulp had a 0.5 percent CED viscosity of 29.7 c.p.s.
  • the pulp had an Elrepho brightness of 88.0 percent and a 0.5 percent CED viscosity of 29.9 c.p.s.
  • the pulp had an Elrepho brightness of 90.4 percent and a 0.5 percent CED viscosity of 18.2 c.p.s.
  • the pulp had an Elrepho brightness of 86.8 percent and a 0.5 percent CED viscosity of 29.1 c.p.s.
  • a process for bleaching a fibrous cellulosic pulp which comprises bleaching the pulp at high consistency and in the form of flutfed or shredded fibers and fiber aggregates with chlorine monoxide in the gaseous phase.
  • a process as claimed in claim Kraft or sulfite pulp 3.
  • reaction period is in the range 1 to 60 minutes.

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US882819A 1968-12-16 1969-12-08 Bleaching of shredded or fluffed cellulosic pulp with gaseous chlorine monoxide Expired - Lifetime US3619349A (en)

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GB59738/68A GB1242709A (en) 1968-12-16 1968-12-16 Bleaching of cellulosic pulp

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US (1) US3619349A (xx)
FI (1) FI50644C (xx)
GB (1) GB1242709A (xx)
NO (1) NO127544B (xx)
SE (1) SE365831B (xx)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3907632A (en) * 1973-10-23 1975-09-23 Ppg Industries Inc Bleaching cellulosic pulps with gaseous chlorine at a pH of 7 to 10 in a multistage bleaching process
US3909194A (en) * 1972-05-30 1975-09-30 Pulp Paper Res Inst Bleaching of textiles with chlorine monoxide
US3990843A (en) * 1974-08-05 1976-11-09 The Dow Chemical Company Method for bleaching raw cotton and cotton textiles
US20030056295A1 (en) * 2001-06-06 2003-03-27 Martin Ragnar Reduction of organically bound chlorine formed in chlorine dioxide bleaching
US20050045291A1 (en) * 2002-08-08 2005-03-03 Martin Ragnar Reduction of organically bound chlorine formed in chlorine dioxide bleaching
US20120180964A1 (en) * 2011-01-14 2012-07-19 The Red Triangle, LLC Compositions and methods for bamboo pulping
US20220267538A1 (en) * 2021-02-24 2022-08-25 Shanghai Jiao Tong University Preparation method and application of porous hydrogel adsorbent based on radix astragali residue

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2178696A (en) * 1938-02-03 1939-11-07 Pittsburgh Plate Glass Co Material treatment
US3074842A (en) * 1959-07-24 1963-01-22 Dorr Oliver Inc Treatment of unbleached cellulose pulps

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2178696A (en) * 1938-02-03 1939-11-07 Pittsburgh Plate Glass Co Material treatment
US3074842A (en) * 1959-07-24 1963-01-22 Dorr Oliver Inc Treatment of unbleached cellulose pulps

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3909194A (en) * 1972-05-30 1975-09-30 Pulp Paper Res Inst Bleaching of textiles with chlorine monoxide
US3907632A (en) * 1973-10-23 1975-09-23 Ppg Industries Inc Bleaching cellulosic pulps with gaseous chlorine at a pH of 7 to 10 in a multistage bleaching process
US3990843A (en) * 1974-08-05 1976-11-09 The Dow Chemical Company Method for bleaching raw cotton and cotton textiles
US20030056295A1 (en) * 2001-06-06 2003-03-27 Martin Ragnar Reduction of organically bound chlorine formed in chlorine dioxide bleaching
US20050045291A1 (en) * 2002-08-08 2005-03-03 Martin Ragnar Reduction of organically bound chlorine formed in chlorine dioxide bleaching
US20120180964A1 (en) * 2011-01-14 2012-07-19 The Red Triangle, LLC Compositions and methods for bamboo pulping
WO2012097380A1 (en) * 2011-01-14 2012-07-19 The Red Triangle, LLC Compositions and methods for bamboo pulping
US20220267538A1 (en) * 2021-02-24 2022-08-25 Shanghai Jiao Tong University Preparation method and application of porous hydrogel adsorbent based on radix astragali residue

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FI50644B (xx) 1976-02-02
FI50644C (fi) 1976-05-10
GB1242709A (en) 1971-08-11
NO127544B (xx) 1973-07-09
SE365831B (xx) 1974-04-01

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