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
  • D21C9/1063—Bleaching ; Apparatus therefor with compounds not otherwise provided for, e.g. activated gases

Definitions

• the cellulosic matter may be mechanical pulp (stone or refiner groundwood) which is at a high consistency of from about 15 to about 95%, or a chemical cellulosic pulp which may be unbleached or partially delignified or semibleached and which also is at a high consistency of from about 15 to about 95%.
• the procedure involves flufling the pulp, preferably to form fiber and fiber aggregates having a low density, substantially uncompacted porous fiuffed structure.
• the fluifed pulp is treated with a gaseous mixture containing an active or electronically excited form of aspecific gas, namely nitrogen, helium, neon argon, krypton, xenon, singlet oxygen or high energy triplet oxygen, either alone or in admixture with the normal form of the gas and ammonia, if the gas is active nitrogen, until the pulp has been contacted with a sulficient amount of such form of gas, e.g. at least about 0.1% to a practical upper limit of about 10% by weight, at a low pressure, e.g.. of from about 1 torr to a high pressure, e.g. up to about 10 p.s.i.g., at a temperature ranging between about 20 to about 100 C. for a period of time of approximately 1 to about 60 minutes at a pH from about 0.5 to about 13.
• a gaseous mixture containing an active or electronically excited form of aspecific gas, namely nitrogen, helium, neon argon, krypton
• This invention relates to the delignification and/or bleaching of cellulosic materials.
• the cellulose materials with which the present invention is concerned are mechanical pulp, chemical pulp and semi-chemical pulp.
• Bleaching is a continuation of the cooking process in which the ligneous material and coloring matter remaining in the chemical pulp are removed selectively with as little degradation of the pulp fibers as possible.
• Bleaching of pulp has advanced to a high degree of sophistication involving single stage and multi-stage procedures.
• the choice of bleaching agent has traditionally been dependent on whetherthe pulp is a mechanical pulp or a chemical p p- (2) Description of the prior art Mechanical and groundwood pulps have many desirable characteristics for low-cost papers, e.g. high yield, good bulk, high opacity, and good printing properties.
• the natural brightness of these pulps is, however, too low for the better grades of groundwood content papers.
• the brightness of unbleached groundwood pulp varies with the species, the wood process, its age and its quality.
• Patented Apr. 23, 1974 e.g. two stages P-Hs or Hs-P or three stage Hs-P-Hs systems.
• a “stage” constitutes a phase starting with addition and reaction of a chemical with a pulp, and ending with the washing of the pulp.
• process variables which are dictated by the type of reaction desired in that particular stage, and the operating conditions of the stage. These variables include: percent of chemical added and consumed, chemical concentration, consistency, temperature, time and pH.
• a series of such stages is called a bleaching sequence.
• the first operation for the removal of, lignin and other encrustants-usually following the digestion stage and the subsequent washing stage in a kraft, soda or sulfite process consists in treating the pulp aqueous suspension with elemental chloride; in aqueous solution. Chlorination of the unbleached pulp so changes the ligneous impurities that they become in part soluble in water while, of the portions not readily soluble in water, a part is soluble in alkaline solutions such as dilute sodium hydroxide.
• the bleaching agents traditionally used are chlorine and chlorine dioxide, usually used in a multi-stage process.
• the first step thus usually consists of treating the pulp in an aqueous suspension with chlorine in solution in the aqueous phase.
• Chlorine dioxide may be used either in admixture with the chlorine, or in replacement of the chlorine, in this first stage.
• the products of pulp chlorination and of the oxidative bleaching stages are more soluble in an alkaline medium than in water, and they are generally taken out of the system by an alkaline extraction.
• Caustic soda is the preferred agent, but other alkalis have been used.
• An object, then, of a main aspect of this invention is to provide a pulp bleaching procedure which is equally effective and useful for both mechanical and chemical pulps.
• the invention also aims, in another of its aspects, to provide a simple, effective process for the bleaching of chemical pulp in which a caustic washing step may be eliminated.
• the invention aims, in another of its aspects, for the provision of such a process for both mechanical and chemical pulps where brightness and/or strength proper ties are enhanced.
• a bleaching agent for such improved process is provided by an active or electronically excited form of a gas selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, singlet oxygen and high eergy oxygen triplet.
• a delignification and/or'bleaching of cellulosic matter in a process for the delignification and/or'bleaching of cellulosic matter, the improvement which comprises subjecting such cellulosic matter while it is in the form of a low density substantially uncompacted flulfed structure and at a consistency of about 15% or more to a delignification and/or bleaching amount, e.g., at least about 0.1% by weight of the cellulosic matter on an oven dry basis (o.d.) of an active or electronically excited form of a gas selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, singlet oxygen and high energy oxygen triplet.
• a delignification and/or bleaching amount e.g., at least about 0.1% by weight of the cellulosic matter on an oven dry basis (o.d.) of an active or electronically excited form of a gas selected from the group consisting of nitrogen, helium, neon,
• an active or electronically excited form of a gas selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, singlet oxygen and high energy oxygen triplet refers to any atomic form, and/or any ionic form, and/or any excited form of, the respective gas, namely nitrogen, helium, neon,-argon, krypton, xenon or oxygen, or a combination of these, which is of sufiicient lifetime that it may be removed from the region in which it is formed, or if it is in a static system, remains long enough after the excitation is stopped, to permit reaction with cellulosic matter.
• Active or electronically ex cited nitrogen, helium, neon, argon, krypton or xenon is produced by passing the respective gas through an arc, glow or corona discharge which can occur in various types of equipment.
• the quantity of the active gas produced depends upon the type of equipment, pressure, electric field and current density.
• a process for the bleaching of mechanical pulp which comprises: providing a pulp having a consistency of from about 15 to about 95%; flufiing the pulp; and thereafter treating the fluffed pulp with a gaseous mixture containing an active or electronically excited form of a gas selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, singlet oxygen and high energy oxygen triplet, namely a bleaching amount, e.g. at least about 0.1% by weight to a practical maximum of about 10% by weight, at a low pressure of, e.g. from about 1 torr to a high pressure up to, e.g. about 10 p.s.i.g., at a temperature of from about 20 to about 100 C. for a period of from about 1 to about 60 minutes, and at a pH from about 0.5 to about 13.
• a gaseous mixture containing an active or electronically excited form of a gas selected from the group consisting of nitrogen, helium, neon, argon,
• a process for the bleaching of a fibrous chemical cellulosic pulp which comprises: providing an unbleached or partially delignified or semi bleached pulp at a high consistency of about 15 to about 95%; fiufiing said pulp; and then contacting the fluffed pulp with sufficient active or electronically excited" form of a gas selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, singlet oxygen and high energy oxygen triplet, namely a bleaching amount, in a mixture containing an active or electronically excited form of a gas selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, singlet oxygen and high energy oxygen triplet, with normal gas respectively, or ammonia with active nitrogen, e.g.
• gases may be provided in active or electronically excited stages.
• hydrogen may be so provided by passing it through a corona discharge.
• active hydrogen would be exceedingly and explosively dangerous to use.
• fluorine, chlorine, bromine and iodine may be made active. How ever, their use is not desirable because they add undesirable halide ions to the wood pulp.
• the amount of the active or electronically excited form of a gas selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, singlet oxygen and high energy oxygen triplet used is at least about 0.1% by weight.
• the maximum amount is not critical since any amount will be operative and hence the cost will determine the amount used. A practical amount would hence be of the order of about 7 to about 10% by weight.
• Example 1 Unbleached kraft pulp from coniferous wood, characterized by Kappa number 24 and a 0.5% C-ED viscosity of 19 was pressed to 30% consistency. The pulp was comminuted into fiber and I fiber aggregates using the apparatus described in US. Pat. No. 3,630,828, issued Dec. 28, 1971.
• Example 1(b) The chlorinated pulp was then extracted with dilute sodium hydroxide (2% NaOH on oven dried pulp at consistency for 1 hour at 60 C.). The pulp was then diluted to 1% consistency with deionized water. The washing efiluent was removed from the pulp and the color, BOD and COD measured by appropriate tests. The pulp was then made into handsheets and the brightness, Kappa number and CED viscosity measured. The results obtained are shown in Table I.
• Example 1(c).0ne portion of the unbleached pulp was placed into a rotary vessel. Nitrogen was passed into the rotary vessel for 45 minutes at a rate of 3 liters/min. The pH of the moist pulp was 5.0. The pulp was then washed and made into handsheets and the brightness, Kappa number and CED viscosity measured. The results obtained are shown in Table I.
• Example l(d).-One portion of the unbleached pulp was placed into a rotary vessel. Nitrogen gas 3 liters/ min. at 8 p.s.'i.g. was passed through a corona discharge where it was acted upon by a primary potential of 120 volts. The gaseous mixture of active nitrogen so formed and the carrier nitrogen was passed into the rotary vessel under atmospheric pressure for 45 minutes. The pH of the moist fiuffed pulp at the end of the reaction was 2.7, and the temperature of the pulp was 25 C. The pulp was then diluted to 1% consistency with de-ionized water. The washing efiluent was removed from the pulp and the color, BOD and COD measured by the appropriate tests.
• Example 1(e) The other half of the treated pulp from Example 1(d) above was extracted with dilute sodium hydroxide (2% NaOH o.d. pulp at 10% consistency for 1 hour at 60 C.) and then washed with deionized water at 1% consistency. The washing efiluent was removed from the pulp and the color, BOD and COD measured by appropriate tests. The pulp was then made into handsheets and the brightness, Kappa number and CED viscosity measured. The results obtained are shown in Table I.
• Example 1(h) A sample of the unbleached pulp mentioned previously in Example 1(f) was pressed to 35% consistency, and then shredded in the apparatus disclosed in the above-identified US. patent. A portion of this pulp was treated with an aqueous solution of sodium carbonate (2% sodium carbonate on pulp), and then reshredded and fiuffed as in Example 1, at 30% consistency. The pump was then placed into a rotary vessel. Nitrogen gas, at a rate of 3 liters/min., at 8 p.s.i.g., was passed through a corona discharge, where it was acted upon by a primary potential of volts. The gaseous mixture of active nitrogen so formed and the carrier nitrogen was passed into the rotary vessel at atmospheric pressure for 45 minutes.
• Nitrogen gas at a rate of 3 liters/min., at 8 p.s.i.g.
• Example 1(i) The other half of the active nitrogentreated pulp from Example 1(h) was extracted with dilute sodium hydroxide, 2% NaOH on o.d. pulp, at 10% consistency, for 1 hour at 60 C., and then the pulp was washed. The pulp was then made into handsheets, and the brightness, Kappa number and CED viscosity meas ured. The results obtained are shown in Table I.
• Example 1(1) The nitrogen which was used for the above tests to produce the active nitrogen" was only 99.7% pure, so that the remaining 0.3 could be oxygen.
• the Kappa number of the "active argon-treated pulp was 10.8.
• Example 1(m) indicate the utility of the invention at very low pressures.
• Example l(n).-A portion of the unbleached kraft pulp mentioned in Example 1(m) was placed in a sta tionary reaction tower and evacuated to 1 torr.
• Argon gas 3 liters/min, was passed through the corona discharge where it was acted upon by a primary potential of 55 volts.
• the gaseous mixture of active argon so formed and a carrier gas was passed through the reaction Jerusalem in the corona reaction.
• Example 2(b)--A portion of the untreated comminuted pulp was placed into a rotary vessel which was set in a bath and the temperature maintained at 25 C. Nitrogen gas, 3 liters/min. at 8 p.s.i.g., was passed through a corona dicharge where it was acted upon by a primary potential of 60 volts. In these experiments, the discharge apparatus used was Welsbach laboratory Model T-408.
• the gaseous mixture of active nitrogen so formed and the carrier nitrogen was passed into the rotary vessel at atmospheric pressure for 30 minute.
• the pH of the moist comminuted pulp after treatment was 4.6.
• a portion of the treated pulp was washed and air dried and the brightness measured.
• the brightness tabs were then placed in a hot air circulatory oven at 105" C. for one hour, then conditioned in a constant atmosphere at arelative humidity of 50% at 70 F.
• the brightness after the aging treatment was measured.
• the brightness, the brightness after aging, and the strength properties of the pulp tested on standard handsheets are set out in Table II below.
• Example 2(c) A portion of the untreated comminuted pulp was placed in a rotary vessel which was set in a bath and the temperature maintained at 50 C. Nitrogen gas, 1 liter/min. at 8 p.s.i.g. was passed through a corona discharge where it was acted upon by a primary potential of 120 volts. The gaseous mixture of active nitrogen'so formed and the carrier nitrogen was passed into the rotary vessel at atmospheric presure for 30 minutes. pH of the moist comminuted pulp after treatment was 4.2. A portion of the treated pulp was washed and air dried and the brightness measured. The brightness tabs were then placed in a hot air circulatory oven at 105; C.
• the improvement which comprises subjecting such cellulosic matter, while it is in the form of a low density substantially uncompacted flutfed structure and at a consistency of about 15% or more to a delignification or bleaching with at least about 0.1% by weight of the cellulosic matter on an oven dry basis, of an -active" or electronically excited form of a gas selected from the group consisting of nitrogen, heli- 10.
• reaction conditions are as follows: the pressure of the reaction is from about 1 torr to about 10 p.s.i.g.; the temperature is about 20 C. to about 100 C.; the absorption or reaction time between the active nitrogen and the cellulosic material is about 1 to about 60 minutes; the pH is about 0.5 to about 13; and the active nitrogen is in admixture principally with nitrogen gas.
• a process for the bleaching of stone or refiner groundwood mechanical pulp which comprises: providing the pulp at a consistency of from about to about 95%; flufiing the pulp; and thereafter treating the flutfed pulp with a gaseous mixture containing at least 0.1% by weight of the pulp on an oven dry basis of an active or electronically excited form of a gas selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, singlet oxygen and high energy oxygen triplet, at a low pressure up to a high pressure, at a temperature of not greater than 100 C. for a period of time of about 1 minute to not greater than 60 minutes and at a terminal pH not greater than 13.
• reaction conditions are as follows: the pressure of the reaction is from about 1 torr to about 10 p.s.i.g.; the temperature is about 20 C. to about 100 C.; the absorption or reaction time between the active nitrogen and the cellulosic material is about 1 to about minutes; the terminal pH of the treated cellulosic material is about 0.5 to about 13; and the active nitrogen is in admixture principally with nitrogen gas.

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Cited By (17)

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• 1972
  • 1972-05-29 CA CA143,298A patent/CA973660A/en not_active Expired
• 1973
  • 1973-05-16 US US00360971A patent/US3806404A/en not_active Expired - Lifetime
  • 1973-05-23 AR AR248206A patent/AR200489A1/es active
  • 1973-05-25 SE SE7307413A patent/SE396970B/xx unknown
  • 1973-05-28 BR BR3947/73A patent/BR7303947D0/pt unknown
  • 1973-05-28 AU AU56214/73A patent/AU469963B2/en not_active Expired
  • 1973-05-28 JP JP48059635A patent/JPS5034642B2/ja not_active Expired
  • 1973-05-28 SU SU7301925441A patent/SU578015A3/ru active
  • 1973-05-29 IT IT50277/73A patent/IT1000024B/it active
  • 1973-05-29 FR FR7319406A patent/FR2186572B1/fr not_active Expired
  • 1973-05-29 DE DE2327407A patent/DE2327407C3/de not_active Expired

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