U.S. patent application number 12/092317 was filed with the patent office on 2010-01-14 for pulp and process for pulping.
Invention is credited to Reijo Aksela, Vesa Myllymaki.
Application Number | 20100006245 12/092317 |
Document ID | / |
Family ID | 35458753 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100006245 |
Kind Code |
A1 |
Myllymaki; Vesa ; et
al. |
January 14, 2010 |
PULP AND PROCESS FOR PULPING
Abstract
The invention relates to a new pulp, which is derived from
lignocellulosic material subjected to agitation in an 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.
Inventors: |
Myllymaki; Vesa; (Helsinki,
FI) ; Aksela; Reijo; (Espoo, FI) |
Correspondence
Address: |
CANTOR COLBURN, LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Family ID: |
35458753 |
Appl. No.: |
12/092317 |
Filed: |
November 10, 2006 |
PCT Filed: |
November 10, 2006 |
PCT NO: |
PCT/FI2006/000362 |
371 Date: |
October 10, 2008 |
Current U.S.
Class: |
162/50 |
Current CPC
Class: |
D21C 9/007 20130101 |
Class at
Publication: |
162/50 |
International
Class: |
D21C 3/00 20060101
D21C003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2005 |
FI |
20051145 |
Claims
1. A pulp prepared by a process comprising subjecting a
lignocellulosic material to agitation in an aqueous
tetra-alkylammonium salt solution under microwave irradiation.
2. The pulp according to claim 1, wherein the lignocellulosic
material is softwood or hardwood.
3. The pulp according to claim 1, wherein the content of
tetra-alkylammonium salt in the aqueous tetra-alkylammonium salt
solution is 1-75 wt-%.
4. The pulp according to claim 1, wherein the cation of the
tetra-alkylammonium salt is ##STR00004## wherein R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are independently a C.sub.1-C.sub.30 alkyl,
C.sub.3-C.sub.8 carbocyclic, or C.sub.3-C.sub.8 heterocyclic group;
and the anion of the tetra-alkylammonium salt is halogen,
pseudohalogen, perchlorate, C.sub.1-C.sub.6 carboxylate, or
hydroxide.
5. The pulp according to claim 4, wherein R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are independently C.sub.4 alkyl; and the anion
is hydroxide.
6. The pulp according to claim 1-4, wherein the agitation is
carried out at a temperature between 40.degree. C. and 270.degree.
C.
7. A process for pulping lignocellulosic material, comprising
subjecting a lignocellulosic material to agitation in aqueous
tetra-alkylammonium salt solution under microwave irradiation.
8. The process according to claim 7, wherein the lignocellulosic
material is softwood or hardwood.
9. The process according to claim 7, wherein the content of
tetra-alkylammonium salt in the aqueous tetra-alkylammonium salt
solution is 1-75 wt-%.
10. The process according to claim 7, wherein the cation of the
tetra-alkylammonium salt is ##STR00005## wherein R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are independently a C.sub.1-C.sub.30 alkyl,
C.sub.3-C.sub.8 carbocyclic, or C.sub.3-C.sub.8 heterocyclic group;
and the anion of the tetra-alkylammonium salt is halogen,
pseudohalogen, perchlorate, C.sub.1-C.sub.6 carboxylate, or
hydroxide.
11. The process according to claim 10, wherein R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are independently C.sub.4 alkyl; and the anion
is hydroxide.
12. The process according to claim 7, wherein the agitation is
carried out at a temperature between 40.degree. C. and 270.degree.
C.
13-18. (canceled)
19. The process according to claim 7, wherein the process is
effective to establish partial or complete delignification.
Description
FIELD OF THE INVENTION
[0001] 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.
BACKGROUND ART
Pulp
[0002] 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.
[0003] 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 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, e.g., the
groundwood, soda, SO.sub.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.
[0004] 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, e.g., scrubbers, precipitators, holding ponds, etc., which
minimize the discharge of 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.
[0005] 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.sup.rd edition,
pages 379-391.
[0006] The present pulps can be subdivided into mechanical and
chemical pulps.
[0007] 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.degree. 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. 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 kcal)/ton for normal paper grades.
[0008] Thermomechanical pulp (TMP) is prepared by presteaming the
wood chips to 110-150.degree. 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.sub.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.
[0009] 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.degree. 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] Solutions of sodium sulfide and sodium hydroxide are in
equilibrium:
H.sub.2O+Na.sub.2S.revreaction.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, Na.sub.2O.
The percent of sodium sulfide in the mixture, when both Na.sub.2S
and NaOH are expressed as Na.sub.2O, 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.degree.
C. in the top heating zone and 90 min at 170.degree. C. in the
second zone. Hardwoods require less vigorous conditions primarily
because of the lower initial lignin content.
[0014] 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.
[0015] 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 Na.sub.2S.sub.x (where x is 2-5, depending on the
equilibrium conditions and how much sulfur is added). Sulfur
Na.sub.2S.sub.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.
[0016] One additional pulping method is sulfite pulping. In the
original sulfite pulping process, wood was pulped with an aqueous
solution of SO.sub.2 and lime. Calcium sulfite has very limited
solubility above pH 2, and excess of SO.sub.2 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
SO.sub.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.
[0017] In addition to previously discussed pulping methods there
are some semichemical 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
[0018] 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
heterogeneous 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 (C. R. Strauss; "A combinatorial approach
to the development of Environmentally Benign Organic Chemical
Preparations", Aust. J. Chem. 1999, 52, p. 83-96).
Microwaves in Mechanical Pulping
[0019] 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.sub.2SO.sub.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.
[0020] 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
[0021] 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.
[0022] 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.
[0023] 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
[0024] 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.
[0025] It is an object of this invention to provide a new pulp
material.
[0026] Another object of this invention is to provide a process for
pulping lignocellulosic material.
[0027] A further object of this invention is to provide a process
for softening the lignocellulosic material.
[0028] Further objects will become apparent from the following
description and claims.
[0029] It is known that cellulose can he completely dissolved in
said aqueous tetra-alkylammonium hydroxide solution. It is also
known that wood can be dissolved in ionic liquids in substantial
absence of water.
[0030] 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.
[0031] Unexpectedly, 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.
[0032] By tuning the salt concentration and agitation time, the
delignification could be avoided and simultaneously, the wood
material was dramatically softened.
[0033] 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 delignificated or softened
already after one minute's agitation in microwave field.
DETAILED DESCRIPTION OF THE INVENTION
[0034] According to the invention there is provided a new pulp,
which pulp is derived from lignocellulosic material subjected to
agitation in aqueous tetra-alkylammonium salt solution under
microwave irradiation.
[0035] The agitation can take place with or without stirring of
lignocellulosic material in said solution.
[0036] 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.
[0037] Preferably lignocellulosic material is wood, such as
softwood and hardwood.
[0038] 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 to barking and chipping before agitation of said material
in aqueous tetra-alkylammonium salt solution under microwave
irradiation.
[0039] The lignocellulosic material can pre-treated by impregnating
water or said aqueous tetra-alkylammonium salt solution into the
lignocellulosic material.
[0040] 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
##STR00001##
wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are independently a
C.sub.1-C.sub.30 alkyl, C.sub.3-C.sub.8 carbocyclic, or
C.sub.3-C.sub.8 heterocyclic group, and the anion of the salt can
be halogen, pseudohalogen, perchlorate, C.sub.1-C.sub.6 carboxylate
or hydroxide.
[0041] Preferably, the anion is chloride or hydroxide, most
preferably the anion is hydroxide.
[0042] An especially preferred tetra-alkylammonium salt is the salt
wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are independently
C.sub.4 alkyl, and the anion of the salt is hydroxide.
[0043] 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 F120031156.
[0044] The agitation can be carried out at a temperature between
40.degree. C. and 270.degree. C., preferably at a temperature
between 70.degree. C. and 210.degree. C., and most preferably
between 120.degree. C. and 190.degree. C.
[0045] It is also possible to apply pressure when subjecting
lignocellulosic material to 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.
[0046] 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.
[0047] The pulp according to the invention can be employed as
material for the production of paper, paperboard, fiberboard, and
similar manufactured products
[0048] According to the invention there is also provided 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.
[0049] In the pulping process, the agitation can take place with or
without stirring of lignocellulosic material in said solution.
[0050] 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.
[0051] Preferably, the employed lignocellulosic material is wood,
such as softwood and hardwood.
[0052] 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 to barking and chipping before agitation of said material
in aqueous tetra-alkylammonium salt solution under microwave
irradiation.
[0053] The lignocellulosic material can pre-treated by impregnating
water or said aqueous tetra-alkylammonium salt solution into
lignocellulosic material.
[0054] 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
the tetra-alkylammonium salt is
##STR00002##
wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are independently a
C.sub.1-C.sub.30 alkyl, C.sub.3-C.sub.8 carbocyclic, or
C.sub.3-C.sub.8 heterocyclic group; and the anion of the salt can
be halogen, pseudohalogen, perchlorate, C.sub.1-C.sub.6 carboxylate
or hydroxide.
[0055] Preferably, the anion is chloride or hydroxide, most
preferably the anion is hydroxide.
[0056] An especially preferred tetra-alkylammonium salt in the
pulping process is said salt wherein R.sup.1, R.sup.2, R.sup.3 and
R.sup.4 are independently C.sub.4 alkyl; and anion of the salt is
hydroxide.
[0057] 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.
[0058] In the pulping process according to the invention, the
agitation can be carried out at a temperature between 40.degree. C.
and 270.degree. C., preferably at a temperature between 70.degree.
C. and 210.degree. C., and most preferably between 120.degree. C.
and 190.degree. C.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] The pulped lignocellulosic material can be employed as
material for the production of paper, paperboard, fiberboard, and
similar manufactured products
[0063] According to the invention there is further provided 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.
[0064] In the softening process, the agitation can take place with
or without stirring of lignocellulosic material in said
solution.
[0065] 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, 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.
[0066] Preferably, the employed lignocellulosic material is wood,
such as softwood and hardwood.
[0067] 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.
[0068] The lignocellulosic material can pre-treated by impregnating
water or said aqueous tetra-alkylammonium salt solution into
lignocellulosic material.
[0069] 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 the tetra-alkylammonium salt
is
##STR00003##
[0070] wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are
independently a C.sub.1-C.sub.30 alkyl, C.sub.3-C.sub.8
carbocyclic, or C.sub.3-C.sub.8 heterocyclic group and the anion of
the salt can be halogen, pseudohalogen, perchlorate,
C.sub.1-C.sub.6 carboxylate, or hydroxide.
[0071] Preferably, the anion is chloride or hydroxide, most
preferably the anion is hydroxide.
[0072] An especially preferred tetra-alkylammonium salt in the
softening process is said salt wherein R.sup.1, R.sup.2, R.sup.3,
and R.sup.4 are independently C.sub.4 alkyl; and the anion of the
salt is hydroxide.
[0073] 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.
[0074] In the softening process according to the invention, the
agitation can be carried out at a temperature between 40.degree. C.
and 270.degree. C., preferably at a temperature between 70.degree.
C. and 210.degree. C., and most preferably between 120.degree. C.
and 190.degree. C.
[0075] 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.
[0076] 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.
[0077] 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 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.
[0078] The softened lignocellulosic material can be employed as
material for the production of paper, paperboard, fiberboard, and
similar manufactured products.
[0079] 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
[0080] 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.degree. C.
[0081] 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.degree. C. in a sealed reactor tube
equipped with magnetic stirring bar.
[0082] The agitation resulted in dark brownish solution comprising
long fiber fines. Washing with water gave both bunches of detached
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.degree. C.
[0083] 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.degree. C. in a sealed reactor tube
equipped with magnetic stirring bar.
[0084] The agitation resulted in dark brownish solution comprising
long fiber fines. Washing with water gave both bunches of detached
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.degree. C.
[0085] 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.degree. C. in a sealed reactor tube
equipped with magnetic stirring bar.
[0086] The agitation resulted in dark brownish solution comprising
long fiber fines. Washing with water gave both bunches of detached
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.degree. C.
[0087] 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.degree. C. in a sealed reactor tube
equipped with magnetic stirring bar.
[0088] The agitation resulted in dark brownish solution comprising
long fiber fines. Washing with water gave both bunches of detached
pale beige fibers and the pulp composition resembled that of
example 1.
Example 5
Treatment of Softwood in 40% Aqueous Tetrabutylammonium Hydroxide
in Microwave Field--5 Minutes at 120.degree. C.
[0089] 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.degree. C. in a sealed reactor tube
equipped with magnetic stirring bar.
[0090] The agitation resulted in dark brownish solution comprising
long fiber fines. Washing with water gave both bunches of detached
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.degree. C.
[0091] 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.degree. C. in a sealed reactor tube equipped
with magnetic stirring bar.
[0092] 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.degree. C.
[0093] 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.degree. C. in a sealed reactor tube
equipped with magnetic stirring bar.
[0094] 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.degree. C.
[0095] 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.degree. C. in a sealed reactor tube
equipped with magnetic stirring bar.
[0096] 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.degree. C.
[0097] 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.degree. C. in a sealed reactor tube
equipped with magnetic stirring bar.
[0098] 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.degree. C.
[0099] 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.degree. C. in a sealed reactor tube equipped with
magnetic stirring bar.
[0100] 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
[0101] Approximately 2000 mg of softwood sticks were mixed into 12
ml of aqueous 40% tetrabutylammonium hydroxide (NaOH) solution and
agitated for overnight at 95.degree. C. in a flask equipped with
magnetic stirring bar.
[0102] Also here, the agitation resulted in destruction of fiber
material giving slimy, brownish pieces of organic material with
non-fibrous properties.
* * * * *