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
  • D21C9/001—Modification of pulp properties
  • D21C9/007—Modification of pulp properties by mechanical or physical means
• • 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
  • D21C1/00—Pretreatment of the finely-divided materials before digesting
  • D21C1/06—Pretreatment of the finely-divided materials before digesting with alkaline reacting compounds

Definitions

• the present invention is directed to a new pulp, which is derived from lignocellulosic material subjected to agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation.
• the invention is also directed to a process for pulping lignocellulosic material and to a process for softening lignocellulosic material.
• Pulp is the raw material for the production of paper, paperboard, fiberboard, and similar manufactured products. In purified form, it is a source of cellulose for rayon, cellulose esters, and other cellulose derived products.
• Pulp is obtained from plant fiber and is, therefore, a renewable source. Fibrous plants have been used a source for writing materials, e.g., papyrus, since the earliest Arabic and Egyptian civilizations. The origin of papermaking, which is the formation of cohesive sheet from the rebonding of separated fibers, has been attributed to Ts'ai-Lun in China in 105 AD, who used bamboo, mulberry bark, and rags. The use of wood as a source of papermaking was not commercially applied until the mid-1800s.
• the principal wood-pulping processes in use today e.g., the groundwood, soda, SO 2 , or acid sulfite, and the sulfate or kraft processes were developed in 1844, 1853, 1866 and 1870, respectively. Since their development, the basic processes have been modified and adapted and the technology has been highly refined.
• the wood material Before pulping processes, the wood material is treated by harvesting, barking, chipping and screening processes.
• the purpose of chipping for pulping is to reduce the wood to a size that allows penetration and diffusion of the processing chemicals without excessive cutting or damage to fibers.
• the chips which are ca 20 mm long, are fairly free-flowing and can be transported pneumatically or on belts and then stored in piles or bins. Kirk-Othmer, Encyclopedia of Chemical Technology, 3 rd edition, pages 379-391.
• the present pulps can be subdivided into mechanical and chemical pulps.
• Said mechanical pulps are subdivided into groundwood pulp, thermomechanical pulp (TMP) and chemithermomechanical pulp (CTMP).
• Groundwood pulp is prepared by pressing wet wood against a wetted rotating grindstone, with the axis of the wood parallel to the axis of the wheel. Temperatures in the immediate grinding zone can be 180-190° C. The movement of the water and the removal of pulp controls and dissipates the heat, thus preventing charring of the wood material. After such treatment, the groundwood pulp contains a considerable proportion of (70-80 wt-%) of fiber bundles, broken fibers, and fines in addition to the individual fibers. The fibers are essentially wood with the original cell-wall lignin intact.
• groundwood pulps are obtained in yields of ca 95%, their cost is relatively low.
• the main direct cost other than wood is power, which is ca 49-75 kJ (11,7-17,9 kcal)/ton for normal paper grades.
• Thermomechanical pulp is prepared by presteaming the wood chips to 110-150° C. in order to make them malleable. A thermoplasticization of the wood occurs when it is heated above the glass transition point of wet lignin. When these chips are fiberized in a refiner at high consistency, whole individual fibers are released; separation occurs at the middle lamella and a ribbon-like material is produced from the S 1 layer of the cell wall. The amount of fibrillization depends on the refining conditions and is critical to the properties of the pulp. This material has a high light-scattering coefficient, although it is lower than that of groundwood, and is highly flexible, which gives good bonding and surface smoothness to the paper. The increased proportion of long fibers improves the tearing properties of TMP-pulps, but the fibers in this fraction are stiff and contribute little to bonding. There is much less fiber fragmentation than in groundwood pulps.
• CTMP Chemithermomechanical pulp
• the chips are pretreated by a mild treatment with sodium sulfite at pH 9-10.
• the chips are impregnated with the chemicals, steamed to 130-170° C. and subsequently refined.
• the yield is 90-92%, which is 2-3% lower than in TMP.
• a range of properties can be obtained by adjusting processing variables but in general, CTMP pulp has greater long-fiber fraction and lower-fines fraction than a comparable thermomechanical pulp.
• the intact fibers are more flexible than TMP fibers and, consequently, better sheet-forming and bonding properties are obtained.
• CTMP pulping is reported to be particularly suitable for pulping high-density hardwoods.
• lignin In chemical pulping, sufficient lignin is dissolved from the middle lamella to allow the fibers to separate with little, if any, mechanical action. However, a portion of the cell-wall lignin is retained in the fiber, and an attempt to remove this during digestion would result in excessive degradation of the pulp. For this reason, ca. 3-4 wt-% of lignin is normally left in hardwood chemical pulps and 4-10 wt-% is left in softwood chemical pulps. The lignin is subsequently removed by bleaching in separate processing if completely delignified pulps are to be manufactured.
• the concentration of the cooking liquor in contact with the wood influences the rate of delignification. Because the time required for diffusion of the chemical through the wood structure and the depletion of the reagent concentration as it penetrates the chip, delignification proceeds more slowly at the center of the chip. In order to prevent overcooking of the principal portion of the pulp, digestion is normally halted before the centers of the larger chips are adequately delignified. The resultant pulp thus contains a portion of nondefibered wood fragments, which are separated by screening and returned to the digester or fiberized mechanically.
• the dominant chemical wood-pulping process is the kraft or sulfate process.
• the alkaline pulping liquor or digesting solution contains about 3 to 1 ratio of sodium hydroxide and sodium sulfide.
• the name kraft which means strength in German, characterizes the stronger pulp produced when sodium sulfide is included in the pulping liquor, compared with the pulp obtained if sodium hydroxide alone is employed, as in the original soda process.
• the alternative term, i.e., the sulfate process is derived from the use of sodium sulfate as a makeup chemical in the recovery process. Sodium sulfate is reduced to sodium sulfide in the recovery furnace by organic-derived carbon.
• Aqueous sodium sulfide is therefore a source of hydroxide ions and must be considered in adjusting the chemical charge.
• a system has been developed in the North American industry to put sodium hydroxide and sodium sulfide on an equivalent basis by expressing them both as their equivalent weight to sodium oxide, Na 2 O.
• the chemical charge, liquor composition, time of heat-up and time and temperature of reaction are functions of the wood species or species mix being digested and the intended use of the pulp.
• a typical set of conditions for southern pine chips in the production of bleachable-grade pulp for fine papers is active alkali 18%; sulfidity 25%; liquor to wood-ratio 4:1; 90 minutes at 170° C. in the top heating zone and 90 min at 170° C. in the second zone.
• Hardwoods require less vigorous conditions primarily because of the lower initial lignin content.
• One modification to the kraft process that is being applied commercially is the polysulfide process.
• elemental sulfur is added to a solution of sodium sulfide and sodium hydroxide, the sulfur dissolves and forms a mixture of complexes with the general formula Na 2 S x (where x is 2-5, depending on the equilibrium conditions and how much sulfur is added).
• Sulfur Na 2 S x is an oxidizing agent, which, under the conditions of kraft pulping, converts the hemiacetal function to a relatively alkali-stable aldonic acid.
• the increase in yield in polysulfide process is proportional to the amount of added sulfur to ca 10% based on wood.
• One additional pulping method is sulfite pulping.
• wood was pulped with an aqueous solution of SO 2 and lime.
• Calcium sulfite has very limited solubility above pH 2, and excess of SO 2 gas was maintained in the digester in order to keep the pH below said level.
• the process can be contrasted with the kraft or soda processes as being an acid process.
• bases other than calcium are used with SO 2 solutions, and sulfite pulping refers to a variety of processes in which the full pH range is utilized for all or part of the pulping.
• Magnesium, sodium, and ammonia are used as alternatives to calcium. Magnesium sulfide has decreasing solubility above pH 5, but sodium and ammonium sulfites are soluble at pH 1-14.
• a semichemical process is essentially a chemical delignification in which the chemical processes are stopped at a point where mechanical treatment is necessary to separate fibers from partially cooked chips. Any known chemical process can be used to produce semichemical pulp.
• the pulps although less flexible, resemble chemical pulps more than mechanical pulps because they are not dependent on rupture of the fiber wall for bonding.
• the yield is 60-85% with a lignin content of 15-20%. The lignin is concentrated on the fiber surface.
• Patent CA 2008526 discloses manufacturing of pulps using microwave heating of impregnated lignocellulosic material.
• the impregnation is conducted with state of the art pulping liquor (Na 2 SO 3 -solution) in the presence of catalysts and chelating agent.
• the impregnation of said chemicals is followed by irradiation of resulting material in a microwave-transparent digester. This is followed by a separate mechanical refining step.
• the main advantage of microwave treatment is the reduction of cooking time and consumed energy.
• Scott et al. (TAPPI Fall Technol. Trade Fair, pp. 667-676) have reported a process for “microwaving logs for energy savings and improved paper properties for mechanical pulps”.
• the treatment was conducted as a pretreatment for mechanical pulping without any impregnation of additional chemicals.
• the energy consumption in subsequent mechanical pulping was decreased up to 15% for the highest employed power level.
• the wooden material was softened by the rapid evaporation of water and thus, rapid rupture of the lignocellulosic material.
• FI20031156 discloses a microwave-assisted method to dissolve lignocellulosic material in ionic liquids.
• the dissolution is complete and can be adapted to any kind of lignocellulosic materials, including soft- and hard wood.
• the dissolution must be conducted in substantial absence of water.
• the dissolved material components can be separated from the resulting ionic liquid solution.
• Pulping is a significant and one of the most energy consuming industries in the world. Due to the climate change, continuously growing population, and thus energy consumption, there is a great demand for new, energy-efficient production technologies in all fields of industry. In pulping, elimination or minimization of malodorous sulfur compounds would be an additional asset.
• Another object of this invention is to provide a process for pulping lignocellulosic material.
• a further object of this invention is to provide a process for softening the lignocellulosic material.
• the agitation could be conducted in a manner wherein a complete to substantial delignification took place and cellulose remained intact as bunches of fine, long fibers.
• the present invention accomplishes a new kind of pulp and process for preparing it.
• lignosellulosic material such as wood could be either delignificated or softened already after one minute's agitation in microwave field.
• pulp which pulp is derived from lignocellulosic material subjected to agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation.
• the agitation can take place with or without stirring of lignocellulosic material in said solution.
• the lignocellulosic material can be virtually any kind of lignocellulosic material.
• the primary source of fiber for pulp is wood, such as softwood and hardwood. Other sources include straws, grasses, and canes. Pulp fibers can be principally extracted from any vacular plant found in nature, also nonwood sources such as straws, grasses, e.g., rice, esparto, wheat and sabai; canes and reeds, e.g., primarily bagasses or sugar cane; several varieties of bamboo; bast fibers, e.g., jute, flax, kenaf, linen, ramie, and cannabis; leaf fibers, e.g., agaba or manila hemp and sisal.
• lignocellulosic material is wood, such as softwood and hardwood.
• the lignocellulosic material can be in its original form as found in nature, or it can be partially processed.
• the lignocellulosic material consists of wood chips, i.e., the lignocellulosic wood material has been subjected to barking and chipping before agitation of said material in aqueous tetra-alkylammonium salt solution under microwave irradiation.
• the lignocellulosic material can pre-treated by impregnating water or said aqueous tetra-alkylammonium salt solution into the lignocellulosic material.
• the content of tetra-alkylammonium salt in aqueous tetra-alkylammonium salt solution can be 1-75 wt-%, preferably 5-60 wt-% and most preferably 10-40 wt-%.
• the cation of the tetra-alkylammonium salt is
• R 1 , R 2 , R 3 , and R 4 are independently a C 1 -C 30 alkyl, C 3 -C 8 carbocyclic, or C 3 -C 8 heterocyclic group, and the anion of the salt can be halogen, pseudohalogen, perchlorate, C 1 -C 6 carboxylate or hydroxide.
• the anion is chloride or hydroxide, most preferably the anion is hydroxide.
• An especially preferred tetra-alkylammonium salt is the salt wherein R 1 , R 2 , R 3 and R 4 are independently C 4 alkyl, and the anion of the salt is hydroxide.
• ionic liquids When miscible with water, also other organic ionic compounds can be employed as a salt component when agitating lignocellulosic material under microwave irradiation according to the invention.
• ionic liquids A variation of such ionic compounds, known as ionic liquids is described in F120031156.
• the agitation can be carried out at a temperature between 40° C. and 270° C., preferably at a temperature between 70° C. and 210° C., and most preferably between 120° C. and 190° C.
• the pressure is preferably below 20 Bar, more preferably below 10 Bar, and most preferably between 2 Bar and 9 Bar.
• the agitation time can vary between 1 minute to 24 hours, depending on the employed salt and concentration thereof, nature and concentration of lignocellulosic material, on the agitation temperature as well as possibly applied pressure.
• the pulp according to the invention can be employed as material for the production of paper, paperboard, fiberboard, and similar manufactured products
• a process for pulping lignocellulosic material in which process the lignocellulosic material is subjected to agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation in order to establish partial or complete delignification.
• the agitation can take place with or without stirring of lignocellulosic material in said solution.
• the lignocellulosic material can be virtually any kind of lignocellulosic material.
• the primary source of fiber for pulp is wood, such as softwood and hardwood. Other sources include straws, grasses, and canes. Pulp fibers can be principally extracted from any vacular plant found in nature, also nonwood sources such as straws, grasses, e.g., rice, esparto, wheat and sabai; canes and reeds, e.g., primarily bagasses or sugar cane; several varieties of bamboo; bast fibers, e.g., jute, flax, kenaf, linen, ramie, and cannabis; leaf fibers, e.g., agaba or manila hemp and sisal.
• the employed lignocellulosic material is wood, such as softwood and hardwood.
• the lignocellulosic material can be in its original form as found in nature, or it can be partially processed.
• the lignocellulosic material consists of wood chips, i.e., the lignocellulosic wood material has been subjected to barking and chipping before agitation of said material in aqueous tetra-alkylammonium salt solution under microwave irradiation.
• the lignocellulosic material can pre-treated by impregnating water or said aqueous tetra-alkylammonium salt solution into lignocellulosic material.
• the content of tetra-alkylammonium salt in aqueous tetra-alkylammonium salt solution can be 1-75 wt-%, preferably 5-60 wt-% and most preferably 10-40 wt-%.
• the cation of the tetra-alkylammonium salt is
• R 1 , R 2 , R 3 , and R 4 are independently a C 1 -C 30 alkyl, C 3 -C 8 carbocyclic, or C 3 -C 8 heterocyclic group; and the anion of the salt can be halogen, pseudohalogen, perchlorate, C 1 -C 6 carboxylate or hydroxide.
• the anion is chloride or hydroxide, most preferably the anion is hydroxide.
• An especially preferred tetra-alkylammonium salt in the pulping process is said salt wherein R 1 , R 2 , R 3 and R 4 are independently C 4 alkyl; and anion of the salt is hydroxide.
• the agitation can be carried out at a temperature between 40° C. and 270° C., preferably at a temperature between 70° C. and 210° C., and most preferably between 120° C. and 190° C.
• the pressure is preferably below 20 Bar, more preferably below 10 Bar, and most preferably between 2 Bar and 9 Bar.
• the agitation time can vary between 1 minute to 24 hours, depending on the employed salt and concentration thereof, the nature and concentration of lignocellulosic material, on the agitation temperature as well as possibly applied pressure.
• the pulped lignocellulosic material can be employed as material for the production of paper, paperboard, fiberboard, and similar manufactured products
• a process for softening lignocellulosic material in which process the lignocellulosic material is subjected to agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation.
• the agitation can take place with or without stirring of lignocellulosic material in said solution.
• the lignocellulosic material can be virtually any kind of lignocellulosic material.
• the primary source of fiber for pulp is wood, such as softwood and hardwood.
• Other sources include straws, grasses, and canes.
• Pulp fibers can be principally extracted from any vacular plant found in nature, also nonwood sources such as straws, grasses, e.g., rice, esparto, wheat and sabai; canes and reeds, e.g., primarily bagasses or sugar cane; several varieties of bamboo; bast fibers, e.g., jute, flax, kenaf, linen, ramie, and cannabis; leaf fibers, e.g., agaba or manila hemp and sisal.
• nonwood sources such as straws, grasses, e.g., rice, esparto, wheat and sabai
• canes and reeds e.g., primarily bagasses or sugar cane
• bast fibers e.g., jute, flax, kenaf, linen, ramie, and cannabis
• leaf fibers e.g., agaba or manila hemp and
• the employed lignocellulosic material is wood, such as softwood and hardwood.
• the lignocellulosic material can be in its original form as found in nature, or it can be partially processed.
• the lignocellulosic material consists of wood chips, i.e., the lignocellulosic wood material has been subjected into barking and chipping before agitation of said material in aqueous tetra-alkylammonium salt solution under microwave irradiation.
• the lignocellulosic material can pre-treated by impregnating water or said aqueous tetra-alkylammonium salt solution into lignocellulosic material.
• the content of tetra-alkylammonium salt in aqueous tetra-alkylammonium salt solution can be 1-75 wt-%, preferably 5-60 wt-% and most preferably 10-40 wt-%.
• the cation of the tetra-alkylammonium salt is
• R 1 , R 2 , R 3 , and R 4 are independently a C 1 -C 30 alkyl, C 3 -C 8 carbocyclic, or C 3 -C 8 heterocyclic group and the anion of the salt can be halogen, pseudohalogen, perchlorate, C 1 -C 6 carboxylate, or hydroxide.
• the anion is chloride or hydroxide, most preferably the anion is hydroxide.
• An especially preferred tetra-alkylammonium salt in the softening process is said salt wherein R 1 , R 2 , R 3 , and R 4 are independently C 4 alkyl; and the anion of the salt is hydroxide.
• the agitation can be carried out at a temperature between 40° C. and 270° C., preferably at a temperature between 70° C. and 210° C., and most preferably between 120° C. and 190° C.
• the pressure is preferably below 20 Bar, more preferably below 10 Bar, and most preferably between 2 Bar and 9 Bar.
• the agitation time can vary between 1 minute to 24 hours, depending on the employed salt and concentration thereof, nature and concentration of lignocellulosic material, on the agitation temperature as well as possibly applied pressure.
• lignocellulosic material is only softened, not pulped. Accordingly, no substantial delignification takes place during the softening process according to the invention.
• the lignocellulosic material structure is ruptured and impregnated with aqueous tetra-alkylammonium salt solution in a manner where the energy and/or chemical consumption in subsequent processing steps is decreased.
• the softened lignocellulosic material can be employed as material for the production of paper, paperboard, fiberboard, and similar manufactured products.
• the present invention accomplishes a new pulp, which can be manufactured in a rapid and energy efficient manner.
• the degree of delignification is tunable and resulting pulp is of high quality consisting of fine, long fibers.
• the present also accomplishes a process for softening lignosellulosic material. Said softened, malleable material can then be processed further in a more energy efficient manner. Accordingly, the present invention results in lower energy consumption and thus, environmental benefits. Also formation of malodorous organic sulfur compounds is avoided.
• the employed tetra-alkylammonium salt is a relatively cheap chemical, which is preferably recycled.
• treated lignosellulosic material were sticks of Finnish softwood cut from 20 mm long wood chips.
• the sticks were cut parallel to wood lamellas in order to facilitate long fibers.
• the original reason to cut the sticks was the restricting size of the microwave reactor, namely 5 ml.

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• 2005
  • 2005-11-11 FI FI20051145A patent/FI20051145A0/fi not_active IP Right Cessation
• 2006
  • 2006-11-10 EP EP06807988A patent/EP1954872A1/en not_active Withdrawn
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  • 2006-11-10 CA CA002627265A patent/CA2627265A1/en not_active Abandoned
  • 2006-11-10 WO PCT/FI2006/000362 patent/WO2007054610A1/en active Application Filing
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