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
  • 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
  • D21C9/1073—Bleaching ; Apparatus therefor with O3

Definitions

• the most commonly used reducing agents are hydrosulphides whence bleaching is conducted in the aqueous phase at 3 to 4 percent consistency, at a pH from 4.5 to 6.0, at a temperature of about 60 C. with a 1-hour retention time and normally chelating or sequestering agents are also present.
• oxidizing agents for the bleaching of mechanical pulps are peroxides which in contrast to hydrosulphides involve an alkaline pH, a relatively high pulp consistency of 15 to 25 percent, moderate temperatures of about 60 C., and a retention time of 2 to 3 hours.
• stabilizers such as sodium silicate and magnesium sulphate in the bleach liquor to prevent decomposition thereof and further the mechanical pulp is normally pretreated at low consistency with organic chelating agents, such as sodium diethylenetriamine penta-acetate (DPTA), to remove naturally occurring trace metals in the mechanical pulps.
• DPTA sodium diethylenetriamine penta-acetate
• An object of a broad aspect of this invention is the provision of a process for the bleaching of a mechanical pulp with ozone whereby the brightness and/or the strength properties of the pulp are enhanced.
• a process for the bleaching of pulp comprising carrying out the bleaching on moist pulp, having a consistency of 15 to 60 per cent by weight solids in the form of fiber and fiber aggregates by treating with a gaseous ozone-oxygen or ozone-air mixture, in the presence of a peroxygen compound containing a peroxygen equivalent of 0.025-l.0 per cent by weight, at a temperature of from 20 to C. for a period of from 1 to 60 minutes at a pH offrom 3.5 to 11.5.
• the process comprises adding a small quantity of peroxygen compound containing a peroxygen equivalent of 0.025 1.0 per cent by weight of the dry pulp, then comminuting the pulp to the form of fiber and fiber aggregates having a consistency of 15 to 60 per cent by weight solids and then treating the pulp with a gaseous ozone-oxygen or ozone-air mixture at a temperature of from 20 to 80 C. for a period of from 1 to 60 minutes at a pH offrom 3.5 to 11.5.
• the peroxygen compound may be added during or after the pulp comminution stage.
• the essential feature of the invention is that the bleaching with ozone takes place in the presence of the peroxygen compound while the pulp is in the form of fiber and fiber aggregates.
• the peroxygen compound is added to the unbleached mechanical pulp, either prior to comminution or during comminution, e.g. by spraying the solution on the fiber and fiber aggregates.
• the comminuted pulp, in the form of fiber and fiber aggregates is then passed into a reactor in which it is treated with an ozone-bearing gas for a period of from 1 60 minutes at a pH offrom 3.5 to 11.5.
• the peroxygen compound may be any conventional inorganic peroxide, including hydrogen peroxide and sodium peroxide or organic peroxide including benzoyl peroxide and ditertiarybutyl peroxide.
• the ozone may be prepared in concentration of 4 percent on a weight/weight basis 0 /0, using a commercial laboratory ozonizer, or may be obtained and used (with proper precautions) from pressurized tanks.
• Fluffed mechanical cellulosic pulp (sometimes referred to as shredded mechanical cellulosic pulp) is the product obtained by fragmentation of a mechanical cellulosic pulp into fiber and fiber aggregates or flocks. Each discrete fiber aggregate or flock is spongy, compressible and readily gas permeable. Each of the fiber aggregates or flocks is usually of an average size of about A 1 inch in diameter and presents a fluffed-up, dry appearance even with about 40 percent by weight moisture in the cellulosic pulp.
• One preferred manner of flufiing or shredding the mechanical pulp to the form above-described is provided in Canadian Pat. application Ser. No. 068,411 filed Nov. 26, 1969, now Canadian Pat. No. 869,267 issued Aug. 27, 1971.
• the mechanical pulp may be treated with a peroxide solution of inorganic or organic nature, then comminuted or shredded as described in the above-identified Canadian patent and finally treated with an ozone-bearing gas.
• the resulting oxidized pulp will then have reached a suitable brightness with the strength properties suitably enhanced.
• EXAMPLE I A commercial spruce-balsam mechanical pulp, brightness 57.3 was pressed to 35 percent consistency. The pressed pulp was sprayed with a solution containing hydrogen peroxide (0.2 percent H on o.d. pulp), sodium silicate (2.5 percent Na SiO on o.d. pulp), sodium hydroxide (1 percent NaOl-l on o.d. pulp), magnesium sulphate (0.05 percent MgSO, on o.d. pulp) and water sufficient to reduce the pulp consistency to 30 percent. The pulp was then comminuted into fiber and fiber aggregates.
• hydrogen peroxide 0.2 percent H on o.d. pulp
• sodium silicate 2.5 percent Na SiO on o.d. pulp
• sodium hydroxide 1 percent NaOl-l on o.d. pulp
• magnesium sulphate 0.05 percent MgSO, on o.d. pulp
• EXAMPLE ll A commercial spruce-balsam mechanical pulp, brightness 57.3 was pressed to 35 percent consistency.
• the pressed pulp tary vessel which was set in a bath and the temperature maintained at 40 C.
• a gaseous ozone-oxygen mixture was passed into the rotary vessel so that within 30 minutes time 1 percent ozone on o.d. pulp basis was passed into the vessel.
• the pH of the moist comminuted pulp was 3.5.
• a portion of the bleached pulp was washed and air-dried and the brightness measured.
• the brightness tabs were then placed in a hot air circulatory oven at C. for 1 hour, then conditioned in a constant atmosphere, relative humidity 50 percent at 70 F.
• the brightness and loss of brightness were measured after aging, and the strength properties of the pulp tested on standard handsheets are set out in Table l.
• a process for bleaching of mechanical pulp which comprises adding a peroxygen compound containing a peroxygen equivalent of 0.025 1.0 per cent by weight of the peroxygen compound on the oven dry weight of the pulp to moist pulp having a consistency of to 60 per cent by weight solids and in the form of fiber and fiber aggregates to provide a mixture of said pulp and said peroxygen compound, and thereafter treating, said resultant mixture with a gaseous mixture selected from the group consisting of ozone-oxygen, ozoneair, and mixtures thereof, until the pulp has been contacted with at least about 1 per cent by weight ozone on an oven-dry basis, said treating being conducted at a temperature of from about C. to about 80 C. for a period of from about 1 to about 60 minutes at a pH of from about 3.5 to about 11.5.
• the gaseous mixture comprises ozone oxygen in concentrations of 4 percent on a weight/weight basis 0 /0 10.
• the gaseous mixture has been prepared by passing oxygen through an ozonizer.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)
• Detergent Compositions (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=4085994

Family Applications (1)

Country Status (9)

Cited By (27)

Families Citing this family (2)

Citations (4)

• 1969
  • 1969-11-27 CA CA902861A patent/CA902861A/en not_active Expired
• 1970
  • 1970-03-18 US US20824A patent/US3663357A/en not_active Expired - Lifetime
  • 1970-06-16 NO NO02322/70A patent/NO127410B/no unknown
  • 1970-06-17 GB GB29401/70A patent/GB1274615A/en not_active Expired
  • 1970-06-26 FI FI701810A patent/FI50552C/fi active
  • 1970-07-03 SE SE09278/70A patent/SE354492B/xx unknown
  • 1970-08-05 FR FR7028861A patent/FR2056606A5/fr not_active Expired
  • 1970-11-26 AT AT1065470A patent/AT302012B/de not_active IP Right Cessation
  • 1970-11-26 DE DE2058232A patent/DE2058232C3/de not_active Expired

Patent Citations (4)

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