EP0062539A1 - Method for oxygen delignification - Google Patents

Method for oxygen delignification Download PDF

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Publication number
EP0062539A1
EP0062539A1 EP82301826A EP82301826A EP0062539A1 EP 0062539 A1 EP0062539 A1 EP 0062539A1 EP 82301826 A EP82301826 A EP 82301826A EP 82301826 A EP82301826 A EP 82301826A EP 0062539 A1 EP0062539 A1 EP 0062539A1
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EP
European Patent Office
Prior art keywords
pulp
gas
oxygen
reaction zone
reaction
Prior art date
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.)
Ceased
Application number
EP82301826A
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German (de)
English (en)
French (fr)
Inventor
Larry D. Markham
Edward F. Elton
Vincent L. Magnotta
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.)
Air Products and Chemicals Inc
Black Clawson Co
Original Assignee
Air Products and Chemicals Inc
Black Clawson Co
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Filing date
Publication date
Application filed by Air Products and Chemicals Inc, Black Clawson Co filed Critical Air Products and Chemicals Inc
Publication of EP0062539A1 publication Critical patent/EP0062539A1/en
Ceased 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
    • 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
    • D21C9/1026—Other features in bleaching processes
    • 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
    • D21C9/1068—Bleaching ; Apparatus therefor with O2

Definitions

  • This invention relates to delignifying pulp in the presence of oxygen, and more particularly to an apparatus and process for the efficient addition,,, removal, and recycle of oxygen gas in a pulp delignification system.
  • Oxygen delignification can be carried out on a wide variety of fibrous materials including wood chips and pulp. When carried out on a bleachable grade of pulp, the process is generally referred to as oxygen bleaching.
  • Conventional apparatuses and processes for the oxygen delignification of fibrous material such as cellulosic pulps generally react the materials in a pressurized vertical vessel.
  • One of the problems encountered in oxygen delignification systems is that the partial pressure of oxygen in the vessel is reduced by the presence of air which enters the vessel with the pulp and by other gases which are produced during delignification such as carbon dioxide, carbon monoxide, and hydrocarbon gases.
  • inert gases such as nitrogen and argon may also be introduced along with the oxygen gas into the reaction vessel.
  • the reduced partial pressure of oxygen can have a detrimental effect on delignification resulting not only in a slower reaction rate, but also a reduction in pulp brightness, strength, and other properties. Additionally, the presence of combustible gases such as carbon monoxide and hydrocarbons can be dangerous if their concentration reaches or rises above the lower explosive limit.
  • One method of increasing the partial pressure of oxygen in the reaction vessel is to increase the operating pressure used for the reaction.
  • increased operating pressures require thicker-walled, and therefore more expensive, vessels. Additionally, the danger of gas leakage from the vessel is increased, and the feeding of the pulp into the vessel against this higher pressure becomes more difficult.
  • the partial pressure of oxygen can be increased and the partial pressures of other gases reduced by bleeding gas from the reaction vessel and replacing it with oxygen.
  • this procedure increases oxygen usage and removes heat from the vessel.
  • Temperature control during oxygen delignification can also be a problem due to the exothermic nature of the reaction.
  • the pulp must be preheated prior to its entry into the reactor to a temperature sufficiently high to initiate the oxidation reaction.
  • the heat evolved during the reaction must be controlled to prevent pulp degradation which results from too much heating. .
  • This over-heating problem is especially acute for processes designed to generate a large Kappa number decrease (i.e., 30 units or more) in the pulp.
  • Circulation and cooling of the reactor gas has been used as a method of controlling the temperature within the reactor vessel when operating with high consistency pulp.
  • Hillstrom et al Svensk Paperstid, Vol. 80, pp. 167-70 (April 10, 1977), teach bleeding gas from the top of a vertical delignification reaction vessel to control the content of carbon monoxide and organic gases therein. The carbon monoxide and organic components of the gas are then catalytically oxidized and the gas cooled and recycled back to the reactor vessel.
  • Luthi et al found that the use of countercurrent gas recirculation to achieve adequate temperature control required large gas flows to avoid undesirable hot spots in the vessel and could result in pulp hang-ups. With respect to concurrent gas recirculation, Luthi et al concluded its use for purposes of temperature control is limited by the compaction of pulp which occurs in the reactor vessel. Additionally, in order for concurrent gas movement to occur at a speed greater than the speed of the pulp, the pulp must be of a high (i.e., 30%) consistency. It is well known, however, that high consistency operation can lead to large temperature increases in the pulp during delignification because of the presence of less dilution water to absorb the heat generated.
  • the channeling of pulp in this type of system is illustrated by the residence distribution curve for the 10 ton/day pilot system used by Annergren et al which shows a broad range of residence times for pulp in the reactor as well as an actual mean residence time substantially less than the theoretical residence time.
  • This channeling problem can be expected to be much worse for a larger diameter commercial size reaction vessel.
  • the need exists in the art for an improved means of supply and recirculation of gas in an oxygen delignification system.
  • the need is especially acute for those systems in which large amounts of delignification are desired since the amount of heat and quantity of combustible and diluent gases generated will be large.
  • an oxygen delignification system having at least one substantially horizontal tubular reaction zone having means for introducing pulp at a first end thereof, means for transporting pulp from the first end to the opposite end of the reaction zone, and means for withdrawing the delignified pulp at the opposite end of the reaction zone.
  • Oxygen gas is introduced into the system at a point adjacent the pulp inlet and moves in essentially plug flow in the same direction as the pulp through the system. Bleed gas can be removed from the system at a point adjacent to the pulp outlet.
  • a gas space is maintained at the top of each tube during the delignification reaction so that free movement of gas in essentially plug flow is achieved.
  • the speed of the internal screws controls the retention time of the pulp in the reactor and insures that the pulp moves in plug flow.
  • the pulp level In order to insure the free movement of gas at a speed different from the speed of the pulp, it is essential that the pulp level must be no more than 90% of the total tube volume.
  • the qas will be moving substantially faster near the pulp inlet than near the pulp outlet because of the high rate of oxygen consumption at the start of the reaction, and this gas movement flushes the nitrogen and combustible gases towards the discharge end of the system.
  • the qas which is trapped within the pulp is exchanged with the free gas above the pulp as a result of the action of the conveying screw, which continuously lifts and turns over the pulp mass in the tube.
  • the practice of the present invention optionally provides for bleeding of the gas from the system at a point adjacent the pulp discharge outlet. This bleeding removes from the reactor the gas having the maximum content of non-oxygen gases including potentially explosive gases such as carbon monoxide and hydrocarbons. When relatively small amounts of delignification are desired, bleeding may not be necessary.
  • the process and apparatus of the present invention are applicable to the oxygen delignification of all types of cellulosic materials including wood chips, bagasse, straw, other agricultural materials, ground wood, thermomechanical pulp, chemimechanical pulp, semichemical pulp, rejects and knots from a pulping process, and chemical pulps such as Kraft, soda, and sulfite pulps.
  • the consistency of raw material introduced into the reactor may be from 1% to 35%, and preferably from 8% to 20%.
  • the alkaline liquor used in the delignification reaction may be known alkaline materials used in the art including sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, Kraft white liquor, oxidized Kraft white liquor, green liquor, sodium tetraborate, sodium metaborate, and mixtures thereof.
  • the dosage of alkaline material on the raw material may be varied over a wide range and is generally in the range of from 0.5 % to 30% calculated as Na 2 0 on oven dry raw material.
  • Known protector chemicals such as magnesium compounds can be used if desired to preserve the viscosity and strength of the pulp.
  • the temperature and pressure and retention time used for the delignification reaction can similarly be varied over a wide range. It has been found that temperatures of from 80°-160°C and an oxygen partial pressure of from 1.4 to 21 Kg/cm 2 20-300 psig and retention times of 5-120 minutes will produce suitable delignification.
  • a countercurrent flow of oxygen gas through the reactor may be utilized by injecting gas at a point near the discharge outlet of the reactor. Because of the plug flow characteristics of the gas in both the cocurrent and countercurrent modes of operation, the formation of hot spots and potentially dangerous pockets of gas is eliminated.
  • gas can be bled off and recirculated to each individual tube to achieve precise control of the reaction conditions in each tube.
  • the recirculated gas can be cooled or not as required and can be passed over a catalyst bed to oxidize combustible components thereof prior to its return to a reactor tube.
  • the concentration of combustible gases would be at a maximum in the third tube so that it would be desirable to circulate that gas through a catalyst bed prior to its recycle back into the third tube.
  • pulp at from 1.0% to 35% consistency, and preferably 8% to 20% consistency is introduced into a first substantially horizontal reaction tube 10 by thick stock pump 12.
  • the use of substantially horizontal tubes includes the use of inclined tubes. However, the angle of incline should not exceed approximately 45 degrees to avoid compression and dewatering of the pulp in the lower end of the tube which will interfere with the uniform mixing of oxygen.
  • the reaction vessel is illustrated as a series of substantially cylindrical reactor tubes, a single vessel having a series of reaction zones or noncylindrical tubes such as a twin screw system may be utilized.
  • Pump 12 may be a Moyno progressing cavity pump available from Robbins & Myers, Inc., Sprinqfield, - Ohio.
  • pump 12 may be a Cloverotor pump available from the Impco Division of Ingersoll-Rand Co., Nashua, New Hampshire, or a thick stock pump manufactured by Warren Pumps, Inc., Warren, Massachusetts.
  • steam Prior to introducing the pulp into thick stock pump 12, steam may be injected into the pulp via line 14.
  • the steam aids in expelling excess air- from the pulp and also raises the temperature of the pulp somewhat.
  • This addition of alkaline material can be made through line 16.
  • the alkaline material serves to lubricate the pulp for easier pumping as well as to insure that the pulp will have an alkaline pH when it enters reaction tube 10. Alternatively, all of the charge may be added at this point.
  • the total alkaline material charge will amount to from 0.5 to 30% by weight calculated as Na 20 of the oven dry weight of the raw fibrous material.
  • alkaline materials suitable for use in this invention include sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, oxidized Kraft white liquor, green liquor, sodium tetraborate, sodium metaborate, and mixtures thereof. Other known alkaline pulping liquors may also be used.
  • the temperatures and pressures used for the delignification reaction can similarly be varied over a wide range. It has been found that temperatures of from 80°-160°C, an oxygen partial pressure of from 1.4 to 21 Kg/cm 2 (20-300 psig) and retention times of 5-120 minutes will produce a suitable level of delignification.
  • alkaline liquor is injected through line 20 and sprayed over the pulp along the length of the tube.
  • the alkaline liquor gradually along the length of the tube rather than all at once as is conventional in high consistency-(i.e., 20-35% consistency) oxygen delignification, better pulp viscosity and strength is achieved.
  • Another advantage to adding the alkaline liquor gradually is that the exothermic delignification reaction is more easily controlled, and the risk of localized overheating is diminished.
  • Oxygen gas is added to the system at a point adjacent the pulp inlet through line 22 where it is mixed with the pulp and alkaline liquor.
  • adjacent the pulp inlet it is meant that oxygen is added to the system prior to midway along the - length of the reactor tube.
  • the oxygen gas is of high purity (i.e., typically 95% purity) although lower purity oxygen can also be used.
  • the oxygen is injected at or near the base of reaction tube 10.
  • Mixing and transport of the pulp and alkaline liquor is achieved by rotating timing screw 24 by a suitable drive means 26.
  • Screw 24 can be of a design conventional in the art, for example, a solid helical flight design. The speed of rotation of screw 24 can be varied to control the retention time of the pulp in the reactor and insures that the pulp is transported forward in essentially plug flow.
  • a gas space is maintained at the top of reaction tube 10 so that the oxygen gas can freely move forward in plug flow at a speed different from the speed of the pulp. It has been found that operation of the system with the reaction tubes less than full and preferably from 50-90% filled, produces acceptable results. The achievement of plug flow is especially important during the initial stages of delignification to insure that the pulp of highest lignin content is exposed to the gas of highest oxygen content. The continuous movement of gas and pulp along the length of the reaction tube and the exchange between gas trapped in the pulp and free gas above the pulp prevents the formation of hot spots or pockets of potentially explosive gases and enhances the uniform delignification of the pulp. It has been found that maintaining an oxygen partial pressure of from between 1.4 to 21 Kq/cm 2 (20. and 300 psiq) results in an acceptable level of deliqnification.
  • reaction tube 10 After traversing the length of reaction tube 10, the pulp, oxygen, and alkaline liquor mixture is removed at outlet 11 and is then introduced into one or more subsequent substantially horizontal reaction tubes such as reaction tube 30.
  • An internal timing screw 32 driven by suitable drive means 34 continuously mixes and transports the mixture along the length of the reaction tube. Aqain, the speed of rotation of the timing screw can be varied to control the retention time and the level of the pulp and allow for adequate delignification. Further reaction tubes (not shown) may be utilized if necessary.
  • reaction tube 30 As the delignified pulp approaches the outlet 31 at the end of reaction tube, 30, partial pressure of oxygen is at its minimum while the partial pressures of reaction product gases such as carbon dioxide, carbon monoxide, and hydrocarbons are at a maximum.
  • the pulp is withdrawn from reaction tube 30 and passed to a cold blow region 35 where it is contacted with dilution water or liquor from line 36.
  • Gas may optionally be vented from the system through line 38 at a point adjacent the discharge outlet of reaction tube 30. In this manner, gas having the least amount of oxygen and the greatest amount of diluent gases is discharged from the system.
  • a countercurrent flow of oxygen gas throuqh the reactor tubes can be utilized.
  • an inlet ' 50 located at the base of reaction tube 30 near its discharge outlet, can be used to inject oxygen gas into the system.
  • the gas will flow in plug flow through the reaction tubes, but in the opposite direction from the direction of pulp flow.
  • This countercurrent flow mode of operation produces both acceptable delignification and good pulp viscosity while avoiding the formation of hot spots and gas pockets.
  • a gas vent 52 may be provided near the pulp inlet to reaction tube 10 to bleed gases.
  • a portion of the gases vented from tube 30 through line 38 is sent through a catalyst bed 40.
  • Catalyst bed 40 acts to oxidize carbon monoxide and other potentially explosive hydrocarbon gases produced as a result of the delignification reaction.
  • the treated gases which contain oxygen as well as carbon dioxide, are then recirculated to tube 30 via line 42 which is in fluid communication with conduit 44. Gases may be vented through vent 54 or may be recirculated back to inlet 22 as shown. If the delignification system comprises a multiplicity of reaction tubes, gas from each tube may be catalytically treated and recirculated to the same or other tubes.
  • simultaneous cocurrent and countercurrent gas flow schemes are contemplated in which oxygen is supplied at or near the midpoint of a reaction tube or series of tubes.
  • Other possible arrangements will be apparent to those skilled in this art including treatment and recirculation of gas flowing countercurrently to the direction of pulp flow.
  • Fig. 3 where like reference numerals represent like elements, the natural draft created by pulp falling through vertical conduit 44 between tubes 10 and 30 is utilized to draw gas vented from tube 30 through catalyst bed 40. Since heat is generated by the catalytic reaction, the heated gas will tend to rise. Thus, gas recirculation lines 38 and 42 as well as catalyst bed 40 are inclined upwardly to aid in the natural recirculation effect. A baffle 46, or other suitable means, prevents pulp from entering conduit 42. Alternatively, a steam ejector or other conventional method may be used to recirculate the treated gas. A vent tube 58 may be provided downstream of the catalyst bed to serve as a means to purge carbon dioxide and inert gases from the apparatus.
  • a softwood thermomechanical pulp was delignified with oxygen and alkali at 8% pulp consistency and 160°C.
  • the total reaction time was 60 minutes and an alkali dosage of 30% sodium carbonate was used on the pulp.
  • the reactor was a horizontal tubular vessel having a horizontal shaft therethrough equipped with paddle flights and rotated at a low speed.
  • the partial pressure of steam at the reaction temperature was 5.25 Kg/cm 2 (75 psig).
  • Countercurrent gas flow was simulated in Run lB by increasing the partial pressure of oxygen from 5.25 Kq/cm 2 (75 psig) at the start of the reaction to 8.75 Kq/cm 2 (125 psig) at the end of the reaction.
  • Run 1B illustrates that a countercurrent oxygen gas flow scheme in a horizontal tubular reactor will produce satisfactory delignification.
  • a softwood sulfite pulp having an initial Kappa number of 69.2 was delignified in the reactor described in Example 1 with oxygen and alkali for a total reaction time of 20 minutes.
  • the consistency of the pulp was 15%, the reaction temperature was 120°C, and the sodium hydroxide dosage was 5.0% by weight based on oven dry pulp.
  • the partial pressure of oxygen was gradually reduced from 4.6 Kq/cm 2 (66 psig) at the start of the reaction to 2.5 Kq/cm 2 (36 psig) at the end of the 20 minute reaction-period.
  • Run 2B the partial pressure of oxygen was gradually increased from 2.5 Kq/cm 2 (36 psig) at the start of the reaction to 4.6 Kq/cm 2 (66 psig) at the end of the reaction time. In both runs the partial pressure of steam in the reactor was maintained at 0.98 Kg/cm 2 (14 psig) throughout the reaction period.
  • Run 2A which simulated a cocurrent oxyqen qas flow had a faster delignification rate (i.e., lower Kappa number), a hiqher pulp brightness, and a qreater selectivity than Run 2B which simulated a countercurrent gas flow.
  • the results reported for Run 2B indicate that satisfactory delignification is obtained for a countercurrent oxygen gas flow scheme in a horizontal tubular reactor.
  • the results of the tests show a rapid delignification rate and a high pulp viscosity (indicative of good strength properties) over a wide range of retention times and production rates.
  • the pulp viscosity was excellent even when degree of deliqnification approached 60%.
  • the results show that oxygen contact with the pulp was good even though only one gas inlet was used in this multiple tube reactor and even though the tests were run at a medium pulp consistency. This is the most difficult consistency range in which to achieve good oxygen contact since the pulp is present as sticky lumps.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Toilet Supplies (AREA)
  • Indicating And Signalling Devices For Elevators (AREA)
  • Water Treatment By Sorption (AREA)
EP82301826A 1981-04-06 1982-04-06 Method for oxygen delignification Ceased EP0062539A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US25140181A 1981-04-06 1981-04-06
US251401 1981-04-06

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EP0062539A1 true EP0062539A1 (en) 1982-10-13

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EP82301826A Ceased EP0062539A1 (en) 1981-04-06 1982-04-06 Method for oxygen delignification

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EP (1) EP0062539A1 (pt)
JP (1) JPS57183489A (pt)
AU (1) AU8191982A (pt)
BR (1) BR8201939A (pt)
CA (1) CA1184709A (pt)
FI (1) FI821185L (pt)
NO (1) NO821139L (pt)
ZA (1) ZA821923B (pt)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5085734A (en) * 1989-02-15 1992-02-04 Union Camp Patent Holding, Inc. Methods of high consistency oxygen delignification using a low consistency alkali pretreatment
US5164043A (en) * 1990-05-17 1992-11-17 Union Camp Patent Holding, Inc. Environmentally improved process for bleaching lignocellulosic materials with ozone
US5164044A (en) * 1990-05-17 1992-11-17 Union Camp Patent Holding, Inc. Environmentally improved process for bleaching lignocellulosic materials with ozone
US5173153A (en) * 1991-01-03 1992-12-22 Union Camp Patent Holding, Inc. Process for enhanced oxygen delignification using high consistency and a split alkali addition
US5174861A (en) * 1990-10-26 1992-12-29 Union Camp Patent Holdings, Inc. Method of bleaching high consistency pulp with ozone
US5181989A (en) * 1990-10-26 1993-01-26 Union Camp Patent Holdings, Inc. Reactor for bleaching high consistency pulp with ozone
US5188708A (en) * 1989-02-15 1993-02-23 Union Camp Patent Holding, Inc. Process for high consistency oxygen delignification followed by ozone relignification
US5211811A (en) * 1989-02-15 1993-05-18 Union Camp Patent Holding, Inc. Process for high consistency oxygen delignification of alkaline treated pulp followed by ozone delignification
US5217574A (en) * 1989-02-15 1993-06-08 Union Camp Patent Holdings Inc. Process for oxygen delignifying high consistency pulp by removing and recycling pressate from alkaline pulp
US5409570A (en) * 1989-02-15 1995-04-25 Union Camp Patent Holding, Inc. Process for ozone bleaching of oxygen delignified pulp while conveying the pulp through a reaction zone
US5451296A (en) * 1991-05-24 1995-09-19 Union Camp Patent Holding, Inc. Two stage pulp bleaching reactor
US5472572A (en) * 1990-10-26 1995-12-05 Union Camp Patent Holding, Inc. Reactor for bleaching high consistency pulp with ozone
US5520783A (en) * 1990-10-26 1996-05-28 Union Camp Patent Holding, Inc. Apparatus for bleaching high consistency pulp with ozone
US5525195A (en) * 1989-02-15 1996-06-11 Union Camp Patent Holding, Inc. Process for high consistency delignification using a low consistency alkali pretreatment

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2006852A (en) * 1977-10-12 1979-05-10 Airco Inc Delignification of wood pulp
EP0030158A1 (en) * 1979-12-03 1981-06-10 The Black Clawson Company Apparatus and process for medium consistency oxygen delignification of pulp

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA918978A (en) * 1970-01-08 1973-01-16 G. Jamieson Allan Oxygen bleaching
JPS5119481B2 (pt) * 1973-08-30 1976-06-17

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2006852A (en) * 1977-10-12 1979-05-10 Airco Inc Delignification of wood pulp
EP0030158A1 (en) * 1979-12-03 1981-06-10 The Black Clawson Company Apparatus and process for medium consistency oxygen delignification of pulp

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
ABSTRACT BULLETIN OF THE INSTITUTE OF PAPER CHEMISTRY, vol.51, no.5, November 1980, Appleton, Wisc. (US) *
TAPPI, Journal of the technical association of the pulp and paper industry, vol.63, no.11, November 1980, Atlanta, G.A. (US) *
TAPPI, vol.61, no.5, May 1978, Atlanta, G.A. (US) *

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5409570A (en) * 1989-02-15 1995-04-25 Union Camp Patent Holding, Inc. Process for ozone bleaching of oxygen delignified pulp while conveying the pulp through a reaction zone
US5188708A (en) * 1989-02-15 1993-02-23 Union Camp Patent Holding, Inc. Process for high consistency oxygen delignification followed by ozone relignification
US5525195A (en) * 1989-02-15 1996-06-11 Union Camp Patent Holding, Inc. Process for high consistency delignification using a low consistency alkali pretreatment
US5211811A (en) * 1989-02-15 1993-05-18 Union Camp Patent Holding, Inc. Process for high consistency oxygen delignification of alkaline treated pulp followed by ozone delignification
US5085734A (en) * 1989-02-15 1992-02-04 Union Camp Patent Holding, Inc. Methods of high consistency oxygen delignification using a low consistency alkali pretreatment
US5217574A (en) * 1989-02-15 1993-06-08 Union Camp Patent Holdings Inc. Process for oxygen delignifying high consistency pulp by removing and recycling pressate from alkaline pulp
US5164044A (en) * 1990-05-17 1992-11-17 Union Camp Patent Holding, Inc. Environmentally improved process for bleaching lignocellulosic materials with ozone
US5164043A (en) * 1990-05-17 1992-11-17 Union Camp Patent Holding, Inc. Environmentally improved process for bleaching lignocellulosic materials with ozone
US5174861A (en) * 1990-10-26 1992-12-29 Union Camp Patent Holdings, Inc. Method of bleaching high consistency pulp with ozone
US5181989A (en) * 1990-10-26 1993-01-26 Union Camp Patent Holdings, Inc. Reactor for bleaching high consistency pulp with ozone
US5472572A (en) * 1990-10-26 1995-12-05 Union Camp Patent Holding, Inc. Reactor for bleaching high consistency pulp with ozone
US5520783A (en) * 1990-10-26 1996-05-28 Union Camp Patent Holding, Inc. Apparatus for bleaching high consistency pulp with ozone
US5863389A (en) * 1990-10-26 1999-01-26 Union Camp Patent Holding, Inc. Pulp bleaching reactor for dispersing high consistency pulp into a gaseous bleaching agent containing ozone
US5173153A (en) * 1991-01-03 1992-12-22 Union Camp Patent Holding, Inc. Process for enhanced oxygen delignification using high consistency and a split alkali addition
US5451296A (en) * 1991-05-24 1995-09-19 Union Camp Patent Holding, Inc. Two stage pulp bleaching reactor

Also Published As

Publication number Publication date
FI821185A0 (fi) 1982-04-05
NO821139L (no) 1982-10-07
FI821185L (fi) 1982-10-07
ZA821923B (en) 1983-02-23
AU8191982A (en) 1982-10-14
BR8201939A (pt) 1983-03-08
CA1184709A (en) 1985-04-02
JPS57183489A (en) 1982-11-11

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