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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/22—Other features of pulping processes
  • D21C3/24—Continuous 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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
  • D21C3/022—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes in presence of S-containing compounds
• • 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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/22—Other features of pulping processes
  • D21C3/222—Use of compounds accelerating the pulping processes

Definitions

• This invention relates to processes for pulping sugarcane bagasse to produce high yield pulp suitable for furnish in the production of newsprint.
• processes for pulping sugarcane bagasse to produce high yield pulp suitable for furnish in the production of newsprint relate to processes involving a controlled prehydrolysis of sugarcane bagasse fibers, followed by a controlled alkaline digestion of the prehydrolyzed product, either with an alkali metal silicate alone or together with other alkaline digestion chemicals, or with other alkaline digestion chemicals alone, followed by treatment with an alkali metal silicate.
• the silicate treatment must be accomplished before or not later than the time that the digested pulp is discharged from the digester to atmospheric pressure.
• the silicate treatment may be applied in the digester blow line or at the digester blow valve.
• the fibrous fraction of sugarcane bagasse like other ligno cellulosic materials (e.g., wood, bamboo, etc.), contains as primary constituents cellulose, lignin and hemicelluloses.
• the latter include both pentosans and hexosans, in amounts averaging about 12 weight percent pentosans (about 90 to 95 weight percent of which is xylan) and about 16 weight percent hexosans (28 weight percent total hemicellulose) based on the total lignocellulosic material in a typical bagasse, on a dry weight basis.
• the relatively high hemicellulose content of the bagasse binds the cellulose fibers together and renders more diificult the production of suitable pulps, particularly due to the inability to break down the fiber bundles, thus resulting in an inordinate amount of shives in the paper made from such pulp.
• the yield from a pulping process is the weight of washed fibers (dry weight basis) recovered after digestion expressed as a percentage of the weight of lignocellulosic material (dry weight basis) originally charged to the pulping process.
• dry weight basis the weight of washed fibers (dry weight basis) recovered after digestion expressed as a percentage of the weight of lignocellulosic material (dry weight basis) originally charged to the pulping process.
• Another object of this invention is to provide a high yield pulping process for producing pulp from bagasse.
• the present invention is based upon the discovery that high yield pulp, having a GE. brightness of greater than about 55 and an opacity greater than about and thus suitable as such for use as newsprint furnish, can be produced from sugarcane bagasse through a process which comprises, as the essential steps:
• the resultant pulp is then refined, screened, washed, etc. in the usual manner prior to its use as furnish to the newsprint paperm-aking machine.
• bagasse fibers used in the practice of the present invention should be as pith-free as is reasonably possible.
• Suitable bagasse fiber feed materials may be prepared, for example, via the use of the apparatus and/ or methods described in U.S. Pat. 3,537,142 issued Nov. 3, 1970' or in my prior copending U.S. application Ser. No. 54,580, filed July 13, 1970 and now U.S. Pat. No. 3,688,345.
• the bagasse fiber feed material be one which has been subjected to a two-stage depithing operation, i.e., first dry depithed in accordance with the aforesaid U.S. Pat.
• the prehydrolysis step be conducted at a carefully controlled pH of from about 4.5 to about 5.8, preferably about 5.2 to about 5.5. At pH below about 4.5 or so the yield from the pulping process is significantly reducedbelow satisfactory economical levels. At higher pH above about 5.9, the desired pre-hydrolysis consumes excessive time, reduces yield and again is economically unattractive.
• Normally fresh bagasse will have a pH in the range of about 6.0 to 6.5 whereas stored bagasse, as a result of acetic acid produced by fermentation during storage, will have a pH in the range of about 4.5 to 5.0.
• the pH during the prehydrolysis step can be maintained within the desired limits of 4.5 to 5.8 or preferred limits of 5.2 to 5.5 in various ways, i.e., by mixing fresh and stored bagasse feed in suitable proportions, by controlling the amount of moisture mixed with the bagasse feed or feeds; by addition of minor amounts of pH adjusting chemicals through use of acid prehydrolysis media such as acid white water (pH about 5.5), etc.
• the prehydrolysis is conducted in the presence of from about 70 to about 100 weight percent water, based on the bone-dry weight of bagasse fiber feed. Additional water required may be present as liquid water or in the vapor form, i.e., steam; preferably as a liquid water-steam mixture which serves to maintain the appropriate temperature as well as furnish the necessary amounts of water. Liquid water may be blended with the bagasse fiber feed prior to introduction to the prehydrolysis reaction zone or in situ in the zone. Added steam is, of course, introduced into the prehydrolysis reaction zone.
• the prehydrolysis reaction is conducted under autogenous steam pressure at temperatures maintained in the range of from about 340 to about 370 Fahrenheit. Temperature is carefully controlled within the said range in order to achieve the desired result of preferentially removing about 40 to 60 percent of the xylan content of the bagasse fiber feed. This will typically correspond to about 4 to 7 weight percent of the total lignocellulosic material fed, dry weight basis. The preferred temperature is about 347 Fahrenheit.
• the desired prehydrolysis reaction can be achieved, under the stated conditions, in a relatively very short period of from about 5 to about 10 minutes.
• the xylan removal is not 100% selective, so that some lignin, hexosans and other pentosans will also be removed. However, the xylan removal is at least preferential under the conditions described, so that any reduction in ultimate yield is held to a minimum.
• the pH of the prehydrolysis medium is raised to at least about 8.5.
• the prehydrolyzed fibers are main tained in this alkaline medium and in the same temperature range as that in the prehydrolysis reaction zone for an additional treatment time of about 5 to or minutes, providing an overall total pulping (i.e., prehydrolysis and alkaline digestion) time of about 15 to about 30 minutes.
• the additional alkaline digestion treatment serves to oxidize, but not remove, lignin components decolored by the initial prehydrolysis reaction.
• the final pulp has a total hemicellulose content of about 20 to 22 weight percent comprised predominantly of hexosans together with less than 60 percent of the original xylan. This is an important feature of the present invention. It has been found that removal of the hexosans will ot improve the important qualities of the final pulp.
• alkaline digestion of the prehydrolyzed bagasse fibers is accomplished by addition of alkali metal silicate, or from about 1 to about 2 percent by weight, based on the weight of bone-dry bagasse fiber feed, of alkali metal bisulfite or a combination of silicate and bisulfite.
• alkali metal silicate or from about 1 to about 2 percent by weight, based on the weight of bone-dry bagasse fiber feed
• alkali metal bisulfite or a combination of silicate and bisulfite may be used together with the bisulfite.
• alkaline chemicals such as sodium sulfite, sodium hydroxide, sodium carbonate, potassium sulfite, potassium hydroxide, potassium carbonate or the like
• the small amounts of alkali metal bisulfite are not overly detrimental to ultimate yields and provide some measure of assistance in improving the brightness of the final pulp.
• An essential step in the process of this invention is the addition to the pulp of about 0.8 to about 1.3, preferably about 1.0 weight percent of an alkali metal silicate, based on the bone-dry weight of the initial bagasse fiber feed.
• This serves to improve the brightness and opacity of newsprint paper produced from the pulp.
• Silicate in amounts less than about 0.8 weight percent do not improve the brightness and opacity to the desired extent. Amounts greater than about 1.3 weight percent actually begin to degrade the pulp by inducing lignin breakdown and consequent yellowing of the pulp. In addition, ultimate pulp yields will be reduced and there is an undesirable reduction in opacity of newsprint produced from the pulp.
• alkali metal silicate or a portion thereof may be added as part or all of alkaline digestion chemicals. Alternately all or part of the required amount of silicate may be added to the pulp separately from the digestion treatment prior to release of the digestion pressure.
• the prehydrolyzed bagasse fibers are digested in alkaline medium containing sodium bisulfite, and all of the required alkali silicate is added in the digester blow line or at the digester blow valve, just prior to final completion of the digestion reaction, serving to simultaneously improve the pulp brightness and opacity.
• sodium silicate such as sodium orthosilicate, sodium sesquisilicate or sodium metasilicate
• sodium silicate is available commercially with various ratios of Na O:SiO such as, sodium orthosilicate having a ratio of Na O 1 SiO,
• pulps which exhibit satisfactory color and brightness properties may be obtained by using other alkali metal silicates such as potassium silicate and lithium silicate, and, in general, it is contemplated that all of the various forms of the alkali metal silicates such as potassium orthosilicate, potassium metasilicate, lithium orthosilicate, and lithium metasilicate will function in a manner which, in this respect, is similar to sodium orthosilicate or sodium metasilicate.
• Com merically available potassium silicates having ratios of K OzsiO corresponding to those for sodium silicates are useful as are those having ratios of K O:SiO of 1:2.1, 1:2.2, 1:2.5 etc.
• the process of this invention is most desirably conducted in a continuous manner, using for this purpose pressure vessels known in the pulp and paper industry as continuous digesters (see, for example, Kirk-Othmers Encyclopedia of Chemical Technology, second edition, vol. 16 (1968), pp. 700-701, and Rydholm Pulping Processes, Interscience Publishers (1965), pp. 343- 355); suitably modified, where required, to permit introduciton of treatment chemicals at the appropriate point or points in the process.
• the pulp is further processed in the usual manner, e.g., refined, screened, washed, etc. prior to use as furnish to the production of newsprint or sale to others for such use.
• pulp was prepared from bagasse fibers using a commercially available continuous two tube digester from Pandia, Inc. Water is added to the fiber feed in a wetting tank and the Wetted mass is screw fed to the digester. Total average residence time in the digester during the run was about 26 minutes. Digested pulp is sent to an Asplund refiner and thence to a blow tank where pressure is reduced to 0.5 pound per square inch gauge. The stock is diluted in the blow tank and then pumped through subsequent processing equipment (a cleaner, a centrisorter and three sequentially connected washers) and finally to storage tanks where it is held until fed to a paper making machine.
• processing equipment a cleaner, a centrisorter and three sequentially connected washers
• the digester was adapted for introduction of digestion chemicals and/ or other additives at various points along the length of the line of travel through the digester In this run provision was made for introduction of digestion (cooking) chemicals at points A to /3 from the beginning of the total digester length and for introduction of sodium silicate at the end of the digester, before the digested pulp passed through the Asplund refiner.
• bagasse fiber feed to the digester was wet depithed bagasse prepared in accordance with earlier US. application Ser. No. 54,580 (US. Pat. 3,688,- 345) referred to above.
• the fiber had a moisture content of about 50% and contained about 23% lignin and 26% total hemicelluloses on a dry weight basis.
• the bagasse fibers were fed to the digester at a rate of about 7.5 tons per hour (bone-dry basis) and were prehydrolyzed at steam pressures of 125 pounds per square inch gauge (about 345 Fahrenheit) in the initial to /3 portion of the digester with clear white water having a pH of 5.5 in amounts sufiicient to provide about 80 weight percent water in the prehydrolysis zone, based on bone-dry weight of the fiber feed.
• the pH of the digestion medium was then raised by introduction of digestion chemicals through the introduction means referred to previously.
• the digestion chemicals used comprised an aqueous solution having a pH of 11 and containing 46 grams per liter caustic soda (NaOH) 185 grams per liter sodium bisulfite (NaHSO and 19 garms per liter sodium carbonate, which was introduced to the digester at a rate of 24.8 gallons per minute.
• NaOH caustic soda
• NaHSO sodium bisulfite
• 19 garms per liter sodium carbonate which was introduced to the digester at a rate of 24.8 gallons per minute.
• a 4% aqueous solution of sodium metasilicate was fed into the pulp at a rate of one gallon per minute before the pulp is passed through the Asplund refiner and thence to the blow tank.
• the run was conducted for an operating period of about 13 hours under the conditions stated, during which period the yield from the digester was 60-65 percent.
• the pulp produced had a GE. brightness of 58-60.
• the resultant pulp had a GE. brightness not greater than 45-46.
• step (b) Process as defined in claim 3 wherein the alkaline digestion chemicals employed in step (b) are predominantly sodium bisulfite and all of the required silicate is added in step (c) as sodium metasilicate in an amount of about 1.0 weight percent.
• step (b) is combined with step (c) by the use of an alkali metal silicate as the sole alkaline pH adjusting material in step (b).

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• Inorganic Chemistry (AREA)
• Paper (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22528372

Family Applications (1)

Country Status (8)

Cited By (5)

Families Citing this family (1)

• 1971
  • 1971-06-01 US US00149000A patent/US3738908A/en not_active Expired - Lifetime
• 1972
  • 1972-05-18 AU AU42450/72A patent/AU474222B2/en not_active Expired
  • 1972-05-19 AU AU42510/72A patent/AU475331B2/en not_active Expired
  • 1972-05-29 BR BR003417/72A patent/BR7203417D0/pt unknown
  • 1972-05-29 BR BR003416/72A patent/BR7203416D0/pt unknown
  • 1972-05-30 EG EG220/72A patent/EG10779A/xx active
  • 1972-05-31 ES ES403376A patent/ES403376A1/es not_active Expired
  • 1972-05-31 FR FR7219543A patent/FR2154407B1/fr not_active Expired
  • 1972-06-01 JP JP5385472A patent/JPS5539678B1/ja active Pending
  • 1972-06-26 PH PH13571*UA patent/PH9628A/en unknown

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