EP1954872A1

EP1954872A1 - A new pulp and process for pulping

Info

Publication number: EP1954872A1
Application number: EP06807988A
Authority: EP
Inventors: Vesa MYLLYMÄKI; Reijo Aksela
Original assignee: Kemira Agro Oy; Kemira Oyj
Current assignee: Kemira Oyj; Yara Suomi Oy
Priority date: 2005-11-11
Filing date: 2006-11-10
Publication date: 2008-08-13
Also published as: BRPI0618527A2; NO20082535L; RU2008120137A; FI20051145A0; CN101305127B; RU2401352C2; WO2007054610A1; CN101305127A; CA2627265A1; JP2009516086A; KR20080083114A; US20100006245A1

Abstract

The invention relates to a new pulp, which is derived from lignocellulosic material subjected for agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation. The invention relates also to a process for pulping lignocellulosic material and to a process for softening lignocellulosic material. The treated material is preferably wood, softwood or hardwood.

Description

A new pulp and process for pulping

Field of the invention

The present invention is directed to a new pulp, which is derived from lignocellulosic material subjected for 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.

Background art Pulp

Pulp is the raw material for the production of paper, paperboard, fϊberboard, 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, eg. papyrus, since the earliest Babylonian 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, eg, the groundwood, soda, SO2, 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.

As with most industries, the environmental and energy concerns of the 1970s effected large changes in the operation of pulp and paper mills as well as much research effort to develop the most energy-efficient and cleanest methods for the production. In most cases, the practical result for the short term has been add-on methods, eg. scrubbers, precipitators, holding ponds, etc, which minimize the discharge off effluents. Other trends have been the increasing use of high yield pulps by modifying the ground wood processes to improve pulp quality, the use of more of the tree in harvesting and chipping, and elimination or minimization of malodorous sulfur compounds in pulping and the toxic and corrosive chlorine compounds from bleaching.

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 ⁰C. 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. They are, therefore, very stiff and bulky and do not collapse like the chemical-pulp fibers. Since 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 kcl)/ton for normal paper grades.

Thermomechanical pulp (TMP) is prepared by presteaming the wood chips to 110- 150 ⁰C 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 flberized in a refiner at high consistency, whole individual fibers are released; separation occurs at the middle lamella and a ribbonlike material is produced from the S₁ 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 pupls.

Chemithermomechanical pulp (CTMP) is prepared in the same manner as TMP but the chips are pretreated by a mild treatment with sodium sulfite at pH 9-10. In the process, 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 shhet-forming and bonding properties are obtained. CTMP pulping is reported to be particularly suitable for pulping high-density hardwoods.

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 ceϊl-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, ie, the sulfate process is derived from the use of sodium sulfate as a makeup chemical in the recovery process. Sodium sulfate is reduced into sodium sulfide in the recovery furnace by organic-derived carbon.

Solutions of sodium sulfide and sodium hydroxide are in equilibrium:

H₂O + Na₂S =Ϊ^ NaHS + NaOH

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, Na₂O. The percent of sodium sulfide in the mixture, when both Na₂S and NaOH are expressed as Na₂O, is known as the sulfidity. 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 ⁰C in the top heating zone and 90 min at 170 °C in the second zone. Hardwoods require less vigorous conditions primary because of the lower initial lignin content.

Although the kraft process is a highly developed, adaptable, and efficient process, there are some problems and disadvantages for its use. Efforts are being made in individual mills to minimize energy, water, and chemical requirements. Additionally, there are two problems inherent in the chemistry of the process, namely low carbohydrate yield and the formation of malodorous organic sulfur compounds.

One modification to the kraft process that is being applied commercially is the polysulfide process. When 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 Na₂S_x (where x is 2-5, depending on the equilibrium conditions and how much sulfur is added). Sulfur Na₂S_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. In the original sulfite pulping process, wood was pulped with an aqueous solution of SO₂ and lime. Calcium sulfite has very limited solubility above pH 2, and excess of SO₂ gas was maintained in the digester in order to keep the pH below said level. Thus, the process can be contrasted with the kraft or soda processes as being an acid process. Currently, bases other than calcium are used with SO₂ 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.

In addition to previously discussed pulping methods there are some semicheniical pulping methods. The distinctions between semichemical and high yield chemical processes are very small and are more a matter of gradation between the mechanical and full chemical processes. 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.

Microwaves

It is known from the recent literature concerning organic synthesis that the reaction times of the organic reactions are remarkable reduced when the energy necessary for the occurrence of the reaction is introduced to the system by using microwave irradiation. The commonly used frequency for microwave energy is 2.45 GHz. There is a wide and continuously increasing literature available in the area of using microwave techniques in organic synthesis. An example of a short summary article of this topic was published by Mingos in 1994(D. Michael P. Mingos; "Microwaves in chemical synthesis" in Chemistry and industry 1. August 1994, pp. 596-599). Loupy et. al. have recently published a review concerning heterogenous catalysis under microwave irradiation (Loupy, A., Petit, A., Hamelin, J., Texier-Boullet, F., Jachault, P., Mathe, D.; "New solvent-free organic synthesis using focused microwave" in Synthesis 1998, pp. 1213-1234). Another representative article has been published by Strauss (CR. Strauss; "A combinatorial approach to the development of Environmentaly Benign Organic Chemical Preparations", Aust. J. Chem. 1999, 52, p. 83-96). Microwaves in mechanical pulping

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 (Na₂SO₃-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. Apparently, the wooden material was softened by the rapid evaporation of water and thus, rapid rupture of the lignocellulosic material.

Microwaves in dissolution of wood and cellulose

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.

Rogers et al. published in 2002 a method for dissolution of pure cellulose fibers into ionic liquids in the microwave field (Swatloski, R.P.; Spear S.K.; Holbrey, J.D.; Rogers, R.D. Journal of American Chemical Society, 2002, 124, p. 4974-4975). Also here, the dissolution must be conducted in substantial absence of water.

Other non-derivatizing organic solvents for cellulose are widely described in "Comprehensive Cellulose Chemistry, Volume 1, Wiley- VCH, page 59-67. Amongst other, aqueous solutions of different tetra-alkylammonium hydroxides have been proved to be efficient solvents for cellulose. A complete dissolution is achieved readily. Since water is always present in excess volumes, said solvents are not practical in derivatization of cellulose. Summary of the invention

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.

It is an object of this invention to provide a new pulp material.

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.

Further objects will become apparent from the following description and claims.

It is known that cellulose can be completely dissolved in said aqueous tetra- alkylammoniumhydroxide solution. It is also known that wood can be dissolved in ionic liquids in substantial absence of water.

When conducting tests to dissolve cellulose in wood material into aqueous tetra- alkylammonium hydroxide solution in microwave field, it was surprisingly found that it was not the cellulose but the lignin in wood material that was dissolved in salt solution.

Unexpectedly, the agitation could be conducted in a manner wherein a complete to substantial delignifϊcation 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.

By tuning the salt concentration and agitation time, the delignification could be avoided and simultaneously, the wood material was dramatically softened.

Both in delignification (pulping) and in softening of lignosellulosic materials, surprisingly short treatment was required in order to achieve said results. The lignosellulosic material such as wood could be either delignifϊcated or softened already after one minute's agitation in microwave field. Detailed description of the invention

According to the invention there is provided a new pulp, which pulp is derived from lignocellulosic material subjected for 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, eg, rice, esparto, wheat and sabai; canes and reeds, eg, primarily bagasses or sugar cane; several varieties of bamboo; bast fibers, eg, jute, flax, kenaf, linen, ramie, and cannabis; leaf fibers, eg agaba or manila hemp and sisal.

Preferably 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. In one preferred embodiment of the invention, 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 of the tetra-alkylammonium salt is

wherein R¹, R², R³ and R⁴ are independently a C₁-C₃₀ alkyl, C₃-C₈ carbocyclic or C₃-C₈ heterocyclic group and the anion of the salt can be halogen, pseudohalogen, perchlorate, C₁-C₆ carboxylate or hydroxide.

Preferably, the anion is chloride or hydroxide, most preferably the anion is hydroxide. An especially preferred preferred tetra-alkylammonium salt is the salt wherein R¹, R², R³ and R⁴ are independently C₄ alkyl and anion of the salt is hydroxide.

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. A variation of such ionic compounds, known as ionic liquids is described in FI20031156.

The agitation can be carried out at a temperature between 4O⁰C and 270⁰C, preferably at a temperature between 7O⁰C and 21O⁰C, and most preferably between 12O⁰C and 19O⁰C.

It is also possible to apply pressure when subjecting lignocellulosic material for agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation. When applied, 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

According to the invention there is also provided a process for pulping lignocellulosic material, in which process the lignocellulosic material is subjected for agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation in order to establish partial or complete delignification.

In the pulping process, 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, eg, rice, esparto, wheat and sabai; canes and reeds, eg, primarily bagasses or sugar cane; several varieties of bamboo; bast fibers, eg, jute, flax, kenaf, linen, ramie, and cannabis; leaf fibers, eg agaba or manila hemp and sisal. Preferably, the employed lignocellulosic material is wood, such as softwood and hardwood.

In the pulping process, 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 of the tetra-alkylammonium salt is

wherein R¹, R², R³ and R⁴ are independently a C₁-C_3O alkyl, C₃-C₈ carbocyclic or C₃-C₈ heterocyclic group and the anion of the salt can be halogen, pseudohalogen, perchlorate, C₁-C₆ carboxylate or hydroxide.

Preferably, the anion is chloride or hydroxide, most preferably the anion is hydroxide.

An especially preferred preferred tetra-alkylammonium salt in the pulping process is said salt wherein R¹, R², R³ and R⁴ are independently C₄ alkyl and anion of the salt is hydroxide.

When miscible with water, also other organic ionic compounds can be employed as a salt component when in the pulping process according to the invention. Applicable compounds are exemplified in FI20031156.

In the pulping process according to the invention, the agitation can be carried out at a temperature between 40⁰C and 27O⁰C, preferably at a temperature between 7O⁰C and 21O⁰C, and most preferably between 12O⁰C and 190⁰C.

In pulping process according to the invention, it is advantageous to choose said parameters in a manner that delignification of lignocellulosic material is partial or complete.

The pulped lignocellulosic material can be employed as material for the production of paper, paperboard, fϊberboard, and similar manufactured products

According to the invention there is further provided a process for softening lignocellulosic material, in which process the lignocellulosic material is subjected for agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation.

In the softening process, the agitation can take place with or without stirring of lignocellulosic material in said solution.

In said softening process, 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, eg, rice, esparto, wheat and sabai; canes and reeds, eg, primarily bagasses or sugar cane; several varieties of bamboo; bast fibers, eg, jute, flax, kenaf, linen, ramie, and cannabis; leaf fibers, eg agaba or manila hemp and sisal.

Preferably, 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. In one preferred embodiment of the invention, 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-alkylammonmm salt solution into lignocellulosic material.

In the softening process according to the invention, 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 of the tetra-alkylammonium salt is

An especially preferred preferred tetra-alkylammonium salt in the softening process is said salt wherein R¹, R², R³ and R⁴ are independently C₄ alkyl and anion of the salt is hydroxide.

In the softening process according to the invention, the agitation can be carried out at a temperature between 4O⁰C and 270⁰C, preferably at a temperature between 7O⁰C and 21O⁰C, and most preferably between 12O⁰C and 19O⁰C.

It is also possible to apply pressure in the softening process according to the invention. When applied, the pressure is preferably below 20 Bar, more preferably below 10 Bar and most preferably between 2 Bar and 9 Bar.

In softening process according to the invention, it is advantageous to choose said parameters in a manner that lignocellulosic material is only softened, not pulped. Accordingly, no substantial delignification takes place during the softening process according to the invention. The lignocelMosic material structure is ruptured and impregnated with aqueous terra-alkylammonium salt solution in a manner where the energy and/or chemical consumption in subsequent processing steps is decreased.

The softened lignocelMosic 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.

Examples

The following examples describe the invention without limiting said invention into examples. In examples 1-10, 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.

Example 1

Treatment of softwood in 40% aqueous tetrabutylammonium hydroxide in microwave field — 5 minutes at 170 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 40% tetrabutylammonium hydroxide solution and agitated for 5 minutes at 170 ⁰C in a sealed reactor tube equipped with magnetic stirring bar.

The agitation resulted in dark brownish solution comprising long fiber fines. Washing with water gave both bunches of detaches pale beige fibers as well as completely separate fibers. Example 2

Treatment of softwood in 20% aqueous tetrabutylammonium hydroxide in microwave field - 5 minutes at 170 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 20% tetrabutylammonium hydroxide solution and agitated for 5 minutes at 170 ⁰C in a sealed reactor tube equipped with magnetic stirring bar.

The agitation resulted in dark brownish solution comprising long fiber fines. Washing with water gave both bunches of detaches pale beige fibers as well as completely separate fibers. The pulp composition was slightly more intact compared to that of example 1.

Example 3

Treatment of softwood in 10% aqueous tetrabutylammonium hydroxide in microwave field — 5 minutes at 170 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 10% tetrabutylammonium hydroxide solution and agitated for 5 minutes at 170 ⁰C in a sealed reactor tube equipped with magnetic stirring bar.

The agitation resulted in dark brownish solution comprising long fiber fines. Washing with water gave both bunches of detaches pale beige fibers and the pulp composition more intact compared to that of example 2.

Example 4

Treatment of softwood in 10% aqueous tetrabutylammonium hydroxide in microwave field - 30 minutes at 170 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 10% tetrabutylammonium hydroxide solution and agitated for 30 minutes at 170 ⁰C in a sealed reactor tube equipped with magnetic stirring bar. The agitation resulted in dark brownish solution comprising long fiber fines. Washing with water gave both bunches of detaches pale beige fibers and the pulp composition resembled to that of example 1.

Example 5

Treatment of softwood in 40% aqueous tetrabutylammonium hydroxide in microwave field — 5 minutes at 120 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 40% tetrabutylammonium hydroxide solution and agitated for 5 minutes at 120 ⁰C in a sealed reactor tube equipped with magnetic stirring bar.

The agitation resulted in dark brownish solution comprising long fiber fines. Washing with water gave both bunches of detaches pale beige fibers as well as completely separate fibers. The pulp composition resembled to that of example 2.

Example 6

Treatment of softwood in 5% aqueous tetrabutylammonium hydroxide in microwave field — 5 minutes at 120 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 5% tetrabutylammonium hydroxide solution and agitated for 5 minutes at 120 °C in a sealed reactor tube equipped with magnetic stirring bar.

The agitation resulted in brownish solution comprising some wooden sticks and long fiber fines. Washing with water gave dramatically softened sticks of wood, some fines detached from said sticks. Example 7

Treatment of softwood in 40% aqueous tetrabutylammonium hydroxide in microwave field — 5 minutes at 80 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 40% tetrabutylammonium hydroxide solution and agitated for 5 minutes at 80 °C in a sealed reactor tube equipped with magnetic stirring bar.

The agitation resulted in brownish solution comprising some wooden sticks and long fiber fines. Washing with water gave dramatically softened and partially detached sticks of wood, some fines being also detached from said sticks.

Example 8

Treatment of softwood in 10% aqueous tetrabutylammonium hydroxide in microwave field — 30 minutes at 80 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 10% tetrabutylammonium hydroxide solution and agitated for 30 minutes at 80 ⁰C in a sealed reactor tube equipped with magnetic stirring bar.

As in example 7, the agitation resulted in brownish solution comprising some wooden sticks and long fiber fines. Washing with water gave dramatically softened and partially detached sticks of wood, some fines being also detached from said sticks.

Example 9

Treatment of softwood in 10% aqueous tetrabutylammonium hydroxide in microwave field - 1 hour at 70 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 10% tetrabutylammonium hydroxide solution and agitated for 1 hour at 70 °C in a sealed reactor tube equipped with magnetic stirring bar. Here, the agitation resulted in transparent, pale brownish solution comprising some wooden sticks. Washing with water gave dramatically softened and partially detached sticks of wood.

Example 10

Comparative treatment of softwood in 40% sodium hydroxide (NaOH) in microwave field — 5 minutes at 170 ⁰C

Approximately 750 mg of softwood sticks were mixed into 4,5 ml of aqueous 40% sodium hydroxide (NaOH) solution and agitated for 5 minutes at 170 °C in a sealed reactor tube equipped with magnetic stirring bar.

Here, the agitation resulted in destruction of fiber material giving slimy, brownish pieces of organic material with non- fibrous properties.

Example 11

Comparative treatment of softwood in 40% aqueous tetrabutylammonium hydroxide without microwave field

Approximately 2000 mg of softwood sticks were mixed into 12 ml of aqueous 40% retrabutylammonium hydroxide (NaOH) solution and agitated for overnight at 95 ⁰C in a flask equipped with magnetic stirring bar.

Also here, the agitation resulted in destruction of fiber material giving slimy, brownish pieces of organic material with non- fibrous properties.

Claims

1. A pulp, characterized in that pulp is derived from lignocellulosic material subjected for agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation.

2. A pulp according to claim 1, characterized in that lignocellulosic material is softwood or hardwood.

3. A pulp according to claim 1 or 2, characterized in that the content of tetra- alkylammonium salt in aqueous tetra-alkylammonium salt solution is 1-75 wt-%, preferably 5-60 wt-% and most preferably 10-40 wt-%.

4. A pulp according to claim 1-3, characterized in that cation of the tetra- alkylammonium salt is

wherein R¹, R², R³ and R⁴ are independently a C₁-C₃₀ alkyl, C₃-C₈ carbocyclic or C₃-C₈ heterocyclic group and the anion of the salt is halogen, pseudohalogen, perchlorate, C₁-C₆ carboxylate or hydroxide.

5. A pulp according to claim 4, characterized in that R¹, R², R³ and R⁴ are independently C₄ alkyl and anion of the salt is hydroxide.

6. A pulp according to claim 1-4, characterized in that the agitation is carried out at a temperature between 4O⁰C and 27O⁰C, preferably at a temperature between 70⁰C and 21O⁰C, and most preferably between 12O⁰C and 19O⁰C.

7. A process for pulping lignocellulosic material, characterized in that lignocellulosic material is subjected for agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation in order to establish partial or complete delignification.

8. A process according to claim 7, characterized in that lignocellulosic material is softwood or hardwood.

9. A process according to claim 7 or 8, characterized in that the content of tetra- alkylammonium salt in aqueous tetra-alkylammonium salt solution is 1-75 wt-%, preferably 5-60 wt-% and most preferably 10-40 wt-%.

10. A process according to claim 7-9, characterized in that cation of the tetra- alkylammonium salt is

11. A process according to claim 10, characterized in that R¹, R², R³ and R⁴ are independently C₄ alkyl and anion of the salt is hydroxide.

12. A process according to claim 7-10, characterized in that the agitation is carried out at a temperature between 4O⁰C and 27O⁰C, preferably at a temperature between 7O⁰C and 210⁰C, and most preferably between 12O⁰C and 19O⁰C.

13. A process for softening lignocellulosic material, characterized in that lignocellulosic material is subjected for agitation in aqueous tetra-alkylammonium salt solution under microwave irradiation.

14. A process according to claim 13, characterized in that lignocellulosic material is softwood or hardwood.

15. A process according to claim 13 or 14, characterized in that the content of tetra-alkylammonium salt in aqueous tetra-alkylammonium salt solution is 1-75 wt- %, preferably 5-60 wt-% and most preferably 10-40 wt-%.

16. A process according to claim 13-15, characterized in that cation of the tetra- alkylammonium salt is

wherein R¹, R², R³ and R⁴ are independently a C₁-C₃₀ alkyl, C₃-C₈ carbocyclic or C₃-Cs heterocyclic group and the anion of the salt is halogen, pseudohalogen, perchlorate, C₁-C₆ carboxylate or hydroxide.

17. A process according to claim 16, characterized in that R¹, R², R³ and R⁴ are independently C₄ alkyl and anion of the salt is hydroxide.

18. A process according to claim 13-16, characterized in that the agitation is carried out at a temperature between 4O⁰C and 27O⁰C, preferably at a temperature between 7O⁰C and 21O⁰C, and most preferably between 120⁰C and 19O⁰C.