Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
  • C01B15/055—Peroxyhydrates; Peroxyacids or salts thereof
  • C01B15/06—Peroxyhydrates; Peroxyacids or salts thereof containing sulfur
  • C01B15/08—Peroxysulfates
• • 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
  • D21C9/1036—Use of compounds accelerating or improving the efficiency of the 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
  • D21C9/16—Bleaching ; Apparatus therefor with per 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
  • 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
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/166—Bleaching ; Apparatus therefor with per compounds with peracids

Definitions

• the invention relates to the field of paper manufacturing and, more particularly, to a process and composition for delignifying a lignocellulosic material, such as chemical wood pulp, using a mixture of monopersulfuric acid and a ketone.
• Pulp is the raw material for the production of paper, paperboard, fiberboard and the like. In purified form, it is a source of cellulose for rayon, cellulose esters and other cellulosic products. Pulp is obtained from plant fiber such as wood, straw, bamboo and sugarcane residues. Wood is the source of 95% of the pulp fiber produced in the United States.
• Dry wood consists of 40 to 50 percent cellulose, 15 to 25 percent other polysaccharides known as hemicelluloses, 20-30 percent lignin, a biopoly er which acts as a matrix for the cellulose fibers, and 5 percent of other substances such as mineral salts, sugars, fat, resin and protein.
• Lignin is composed primarily of methoxylated phenyl propane monomeric units interconnected by a variety of stable carbon- carbon and carbon-oxygen (ether) linkages.
• the lignin of conifers is apparently an oxidative polymerization product of coniferyl alcohol [3-(3' ⁇ methoxy-4 '-hydroxyphenyl)allyl alcohol], while the lignin of deciduous trees appears to be derived from coniferyl alcohol and sinapyl alcohol [3-
• the strength of paper ultimately produced from pulp is dependent upon the chemical integrity of the cellulose, while the color arises from the lignin.
• the desired selectivity will be reflected in a low kappa number (little unbleached lignin) and a high viscosity of the residual pulp (little cleavage of long-chain celluloses) .
• Chemical pulp is manufactured by dissolving the lignin with hot solutions of (1) sodium hydroxide, (2) calcium, magnesium, or ammonium bisulfite, or (3) a mixture of sodium hydroxide and sodium sulfide (made from lime and reduced sodium sulfate) .
• the products known as soda pulp, sulfite pulp or sulfate (kraft) pulp, respectively consist of impure cellulose.
• soda pulp, sulfite pulp or sulfate (kraft) pulp respectively consist of impure cellulose.
• most of the hemicelluloses are also dissolved.
• the yield for chemical pulping is typically 40-60% based on wood weight.
• Mechanical pulps are characterized by their high yield and high lignin content. These pulps are called “mechanical” because a significant amount of mechanical energy (grinding and refining) is required to breakdown the wood chips.
• Chemical pulps contain about 5% lignin (weight basis) while mechanical pulps typically contain greater than 15% lignin. In order to make a white sheet from a chemical pulp almost all of the residual lignin must be removed. This is normally achieved by multistage bleaching using oxidants, some of which [chlorine (Cl 2 ) , chlorine dioxide (C10 2 ) , and sodium hypochlorite (NaOCl) ] contain chlorine.
• oxidants some of which [chlorine (Cl 2 ) , chlorine dioxide (C10 2 ) , and sodium hypochlorite (NaOCl) ] contain chlorine.
• chlorine (Cl 2 ) chlorine dioxide
• NaOCl sodium hypochlorite
• Presently bleached chemical pulp producers are seeking ways of decreasing or eliminating the use of chlorine- containing chemicals, the use of which leads to the formation and subsequent discharge of organochlorine compounds. Regulations to limit the discharge of adsorbable organic halogens (AOX) have already been established in several
• Oxygen is less selective than chlorine and chlorine dioxide and can therefore only be used for partial lignin removal.
• the cellulose is strongly affected, especially when the lignin content is low; therefore, the oxygen treatment must be of short duration.
• Monopersulfuric acid or Caro's acid and its caroate anions have features that are attractive for kraft pulp bleaching: 1) Caro's acid is a more efficient solubilizer of lignin than is H 2 0 2 , 2) it is only marginally more expensive than H 2 0 2 because H 2 S0 4 is the only reactant needed to generate it from H 2 0 2 , and 3) the sulfate anions in the resulting bleaching effluent can be recycled to the kraft recovery system.
• the use of Caro's acid for bleaching pulp is disclosed in U.S. Patents 4,404,061; 4,475,984;
• Dioxiranes are capable of transferring an oxygen atom to a variety of donor compounds yielding an oxidized product and the ketone precursor.
• the invention relates to a process for delignifying a lignocellulosic material, in particular for bleaching wood pulp, most particularly for kraft wood pulp.
• the process comprises exposing the pulp at pH 6.0 to 9.5 to a mixture of monopersulfuric acid and a ketone of formula
• R 1 and R 2 are independently selected from the group consisting of alkyl and aryl, or R 1 and R 2 together form a carbocycle.
• the ketone is present at from 1 to 4% of the dry weight of the pulp; preferred ketones are acetone, methyl ethyl ketone and cyclohexanone; and the pH is optimally maintained at about 7.0.
• An embodiment is characterized in that the kappa number of the wood pulp is reduced by ten or more while the viscosity of the pulp is reduced by less than 5 cp.
• the consistency is from about 1% to about 35% in water and monopersulfuric acid furnishes from 0.1 to 2.0% active oxygen based on the dry weight of the pulp.
• the invention relates to a composition for delignifying a lignocellulosic material comprising in combination:
• R 1 and R 2 are independently selected from the group consisting of alkyl and aryl, or R 1 and R 2 together form a carbocyclic ring;
• the ketone is selected from the group consisting of acetone, methyl ethyl ketone and cyclohexanone and the buffer is sodium bicarbonate.
• the invention relates to pulps that have been delignified by the processes described above and to the corresponding delignification mixtures.
• Chemical pulps may contain acetone and monopersulfuric acid which generate dimethyldioxirane within the pulp.
• Fig. 1 is a graph of kappa number versus % active oxygen based on the weight of the pulp for a composition of caroate only and a composition according to the invention, containing ketone.
• the peroxidic compounds involved each contain one active oxygen atom per molecule.
• Fig. 2 is a graph of kappa number versus % ketone based on the weight of the pulp for two ketones: acetone and methyl ethyl ketone (MEK) .
• the basis of the invention is the discovery that a combination of monopersulfuric acid and ketone provide a superior bleaching composition and process for chemical wood pulp.
• Reaction (1) in scheme B is known and is discussed by Jeyaraman and Murray [J_j_ Am. Chem. Soc. 106, 2462- 2463 (1984)].
• Reaction (2) is known and is the basis of the published PCT application of Lee (WO
• reaction (3) is also known and is the basis of patents cited above.
• the enhanced efficiency and selectivity, as well as the reduced requirements for ketone, of the present invention are believed to arise from the heretofore unknown facility of pathways involving reactions (4) and (5) .
• reaction (6) consumes oxidant without producing product, the facility of reactions (4) and (5) are only observed and realized when reaction (6) is suppressed.
• the amount of residual lignin in a pulp is measured by its kappa number; 0.15 times the kappa number is the weight percent of lignin.
• Softwood pulp coming out of a kraft process has a kappa number of 20 to 30; hardwood pulp is somewhat lower: 10 to 20. It is desirable for most uses to reduce the kappa number as much as possible, but in any event to below about 10 for softwood and about 5 for hardwood. At the same time, the production of paper having a desirable degree of strength requires that the cellulose be minimally degraded.
• the integrity of cellulosic structures is measured by determining the viscosity of a cupri-ethylenediamine solution according to the procedures described in TAPPI standard method T230.
• Softwood pulp coming out of a kraft process has a viscosity, in this test, of about 22 to 40 centipoises (cp) . It is desirable to maintain the viscosity above 15 during delignification.
• the measure of a selective delignification process is thus a high ratio of viscosity to kappa number.
• the effects of pH on the caroate/ketone delignification of the invention were examined.
• the untreated pulp had a kappa value of 27.0.
• a kappa number of 7.2 73% delignification
• pH 8.0 Using acetone as the ketone, a kappa number of 7.2 (73% delignification) was obtained at pH 8.0. Lowering the pH to approximately 7.0 resulted in a pulp with kappa number 4.3 (84% delignification).
• Sodium bicarbonate has been found ideal for buffering the system at pH 7, but sodium carbonate, sodium hydroxide or sodium acetate could also be used.
• pH plays only a minor role in DMD delignification (Note entries 4 and 5, in Table 1.)
• reaction temperatures of 10° C, 25° C, and 50° C were investigated in caroate/acetone delignification of a kraft pulp (kappa, 27.0; viscosity, 27.7 cp) . In all cases, the reaction was complete after 30 minutes and led to equivalent kappa numbers and pulp viscosities after alkaline extraction. Most delignification processes based on peroxidic chemicals are sensitive to transition metals. Therefore, a softwood kraft pulp with kappa number 27.0 and viscosity 27.7 cp was acid-washed and, together with the unwashed pulp, was analyzed for transition metals. (Table 3) .
• cyclohexanone appears to be the most promising.
• a charge of 2.50% on pulp at 2.67% consistency corresponds to an aqueous phase concentration of 0.007 M, ten times lower than the minimum effective concentration for acetone.
• acetone and MEK were more effective than cyclohexanone in lowering the kappa number.
• Di-2-pyridyl ketone and N,N- dimethyl-4-oxopiperidinium nitrate were ineffective
• lignocellulosic species are woody materials, especially tree woods including softwoods and hardwoods
• other lignocellulosic species commonly employed in making pulp and paper may be employed.
• Illustrative of these non-woody species are such materials as grasses, cereal straws, bamboo, cornstalks, sugar cane bagasse, kenaf, hemp, jute, sisal, esparto, reeds and the like.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Paper (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)

Priority Applications (6)

Applications Claiming Priority (2)

Publications (1)

Family

ID=21753173

Family Applications (1)

Country Status (9)

Cited By (4)

Citations (3)

Family Cites Families (1)

• 1994
  • 1994-01-31 CA CA 2154778 patent/CA2154778A1/en not_active Abandoned
  • 1994-01-31 EP EP94907926A patent/EP0681625A4/en not_active Withdrawn
  • 1994-01-31 AU AU61307/94A patent/AU6130794A/en not_active Abandoned
  • 1994-01-31 JP JP6518129A patent/JPH08508791A/ja active Pending
  • 1994-01-31 WO PCT/US1994/001085 patent/WO1994018386A1/en not_active Application Discontinuation
  • 1994-01-31 NZ NZ26200994A patent/NZ262009A/en unknown
  • 1994-01-31 BR BR9405754A patent/BR9405754A/pt not_active Application Discontinuation
• 1995
  • 1995-07-21 NO NO952913A patent/NO952913L/no unknown
  • 1995-07-31 FI FI953651A patent/FI953651A0/fi unknown

Patent Citations (3)

Non-Patent Citations (1)

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