Note: Descriptions are shown in the official language in which they were submitted.
1 t
CA 02654698 2008-12-08
FPCH06160022CA
A method of preparing bleached pulp with high yield by
free radical clean pulping process
Field of the invention
The present invention discloses a method of preparing bleached pulp
with high yield by free radical clean pulping process. More particularly,
the present invention describes a method of preparing clean bleached pulp,
which merely uses free radicals formed from oxygen in an electrochemical
lo vessel without using alkali, chlorine, sulfur, and anthraquinone.
Back ro~ und of the invention
It is well known that the paper-making industry in the world is facing
three severe problems: lacking stock, lagging technology, and severe
pollution. These problems are those in dire need of solutions faced by the
paper-making industry all over the world.
Long term shortage of the paper-making stocks does not involve the
paper-making industry of only a certain local region, but the whole world.
Forest is the lung of the earth life and has the functions of reserving water
source, preventing water and soil loss, regulating climate, and absorbing
carbon dioxide and preparing oxygen, so it possesses not only the
ecological value, but also the economic value. However, according to the
report on the statistic data, the forest area of the world now is decreasing
in a rate of 150,000 km2/year and the area of tropic rain forest is
decreasing in a rate of 0.5 kmZ/min.
China is a country severely poor in wood and forest, for example, the
average area of the forest per capita is only 1/5 of the world average level
(0.128 hm2) and the average reserve of the forest per capita is only 1/8 of
the world average level (9.05 m3). According to the comparison of 2000 to
1999 in "China Forestry Statistic Yearbook", the reduction rate of the
forest was 12.9% for the ten key forestry ecological projects, 10.07% for
the natural forest-protecting project, 6.33% for the mountain-sealing and
-1-
CA 02654698 2008-12-08
forest-raising area, 24.75% for the defending forest, 3.28% for the
economic forest, and 14.07 for the wood-using forest.
The insufficient utilization rate of the non-wood fiber stock such as
rice stalk, wheat stalk, cotton stalk, hybrid giant napier, banana stalk, bast
fiber, etc, is an important reason leading to the shortage of the stock.
According to the latest data in "Assessment of the availability of the
biological resource in China" published in July of 1998, the output of the
crop stalk in 1995 was 604 million tons, wherein the wheat stalk 140
million tons, rice stalk 115 million tons, cotton stalk 14.30 million tons,
and sugarcane residue 6.45 million tons. The amount of the available crop
stalk was 513.4 million tons except the part that directly returned to the
farmland and the part that was consumed during collection, the two parts
accounting for about 15.0% of the total. The stalk used for paper-making
accounted for about 2.3% of the total.
According to the statistic in 1997, rice stalk, wheat stalk, bulrush,
sugar cane residue, and bamboo accounted for 90% of the total amount of
the non-wood stock used for paper-making. The annual output of the major
non-wood stocks and their proportion for pulp preparing are provided in
the following table.
Stock Annual output Proportion for pulp
(Million tons) preparing ( % )
Wheat stalk 102 17
Rice stalk 200 2
Bulrush 2.83 70
Sugar cane residue 16 4
Bamboo 10 /
China is a large agricultural and cotton-producing country and the
annual plant resource comparable to wood is about 160 million metric tons.
During the "Tenth Five Year Plan", the planting area of the national key
cotton-producing regions will be stabilized at 6.0 million hectares in 2010
-2-
1
CA 02654698 2008-12-08
and the output of the annual high quality cotton stalk will be 34.2 million
tons. Calculating based on the data in textbooks, 24.282 million tons of
pulp can be produced per year from cotton stalk alone, and more than 7.4
million tons of pulp can be produced per year if the utilization rate attains
30%, corresponding to the total of the imported pulp per year, but thus far
the utilization rate of such a annual plant resource similar to hardwoods is
less than 1 %.
The textbook, "Fiber Chemistry of Plants" published by China Light
Industry Press in 2001 disclosed data on the chemical analysis of cotton
1o stalk (wt%) and the average fiber length (mm), the results are shown in the
following table.
o y Extractive C) o x o CD >
~= CD ~ ,.., a- 0 ,.~~.,, CD
0 ~O
Z fjq
p p
(D Q (D 0
t:1
Skin 6.12 6.12 18.34 23.66 43.57 2.7 75.57 16.84 23.26 9.64 2.46
Stem 7.87 2.05 3.71 5.02 21.36 1.68 76.32 21.31 18.07 1.42 1.08
Whole 8.12 3.15 7.68 9.74 28.72 1.94 75.95 20.17 19.27 4.25 1.68
A new type stock, Hybrid Giant Napier is a perennial, upstanding, and
1s cespitose grass family plant with an English name of Hybrid Giant Napier
and a formal name of Ponnisetum hydridum, which has come into being by
hybridization and breeding of elephant grass of South America with
pennisetum and takes the first place among the pasturages due to its high
output. After introducing into China from Colombia and successful
20 planting in Hainan in eighties of 20th century, it has been spread
gradually
from the south to the north of China and been planted successively in
Sichuan, Hunan, Jiangsu, Tianjin, Guizhou, Shaanxi, etc. It is proved by
the experiment that Hybrid Giant Napier has the advantages of strong
adaptability, simple planting process, high output, and high content of
-3-
CA 02654698 2008-12-08
cellulose, etc. The analysis of the chemical composition of Hybrid Giant
Napier and the comparison to the composition of wheat stalk, bulrush, and
fast-growing poplar are shown in the following table (%).
o 0
~ 0
~
~ ~ lY =yY lY ~ ~0
CD
\Y
Cr
-ly=.-^ `~
I1 "
0
Hybrid Giant Napier 3.77 4.43 7.61 32.39 4.01 20.82 78.15 19.50
Wheat stalk 8.28 5.36 11.53 42.59 4.37 18.12 68.72 24.04
3.12-
Bulrush 4.52 5.69 32.29 2.63 19.58 76.60 22.15
4.40
2.14 17.84 1.84 22.37 77.35 22.48
0.52-
Fast-growing poplar* - - _ - - _
1.03
3.45 21.88 2.24 23.40 80.62 27.17
Note: *Comparative cellulose
The harvest area of banana in the world was 4.5447 million hectares
in 2003, which was 152 thousand hectares more than the 4.3927 million
hectares in 2002. The country having the largest harvest area of banana is
1o India, being 620.0 thousand hectares, which account for 13.64 % of the
total harvest area of the world; the next is Brazil having 513.2 thousand
hectares, which account for 11.29% of the total harvest area of banana in
the world; the harvest areas of the other major banana-producing countries
are: Philippines 400.0 thousand hectares, Indonesia 345.0 thousand
hectares, China 235.0 thousand hectares, Ecuador 218.7 thousand hectares,
Thailand 139.0 thousand hectares, Vietnam 99.7 thousand hectares,
Mexico 72.6 thousand hectares, Papua New Guinea 62.0 thousand hectares,
and Madagascar 50.0 thousand hectares, respectively.
China is one of the major banana-producing countries in the world
-4-
- .
CA 02654698 2008-12-08
and the major producing regions are Guangdong, Guangxi, Fujian, Hainan,
Yunan, and Taiwan, with the planting area in 2000 being 249 thousand
hectares. Therein Guangdong took the first place, and its planting area
attained 101 thousand hectares with Gaozhou and Zhongshan being its
famous banana-producing regions; Guangxi took the second place, and its
planting area was 59.7 thousand hectares, which was mainly distributed in
Nanning suburb, Pubei, Lingshan, Tianyang, Longan, Tiandong, Longzhou,
etc, with Musa AAA Group Cavendish banana and plantain banana as the
major varieties; Fujian took the third place, and its planting area was 35
Io thousand hectares, which was mainly distributed in Zhangzhou and
Longhai with Tianbao banana as the major variety; Hainan took the fourth
place, its planting area being 33 thousand hectares, which was mainly
distributed in Danzhou, Dongfang, Ledong, etc with Musa AAA Group
Cavendish banana as the major variety; the planting area of banana in
Yunnan was mainly distributed in Hekou, Yuanyang, Xishuangbanna, etc
with Musa AAA Group Cavendish banana as the major variety.
The bast fiber stock comprises two varieties. The first one is the bark
of the tree, which is of great value for paper-making because the bark layer
of part of trees contains rather much fiber, e.g., the mulberry branch bast
fiber, which is a high quality stock for paper-making, accounts for
26%-30% of the total weight of the whole branch, but contains less lignin.
The other variety is hemps, the utilization rate of which in paper making is
extremely low due to the restriction by many factors.
The paper-making industry still uses the traditional paper-making
technology of more than 100 year ago, which uses large amounts of strong
acids, strong alkali, strong chlorine, strong sulfur, and anthraquinone,
discharges black liquid with a CODCr up to 180,000 mg/L, has a long
technological flow, lagging technological equipments, and the need for a
vast investment on the equipment and a high environment protection cost.
The oxidation bleaching method may date back to early fifties of 20th
century. Wood and forest Chemists, Nikieih and Arim of Soviet Union
discovered in 1952 that oxygen could bleach for the first time. 12 years
-5-
CA 02654698 2008-12-08
later, in 1964, French scientists, Rebeve et al used magnesium salts to
protect cellulose from oxidative degradation. Three countries, America,
France, and Switzerland successively established laboratories in 1970, and
the first chlorine dioxide bleaching workshop in the world was established
at Enstrd, Southern Africa in the same year. In 1972, America established
an oxygen bleaching workshop with a daily output of 12 tons and applied
for a patent of non-chlorine bleaching, which was not put into
commercialization due to severe loss of cellulose, high energy and water
consumption, and a high production cost. 27 years later, French George
Rood Company and American Pwessl Company successively started using
chlorine dioxide combined with ozone again for bleaching in 1999 and
2001, respectively, still unable to get rid of pollution by chlorine, which
was proved to be able to form carcinogens (such as chloroform, carbon
tetrachloride, trichloromethane, etc) when heated. By march of 2003, the
paper-making industry in the world had never got rid of steaming ball and
bleaching tower technologies leading to severe pollution of alkali, chlorine,
sulfur, and anthraquinone, and the treatment of chromophore group of
lignin had still rested on the traditional technology of 100 years ago which
separated and degraded lignin. In recent years, many countries even use
caustic soda anthraquinone method without restraint. Condensed ring
arenes in anthracene series arenes are now affirmed to have carcinogenesis
and ascribed to carcinogens by the World Environment Protection
Organization long ago. Therefore, the paper-making industry in the world
has become an object specially attended by environment protection
organizations.
The traditional technology has a long flow: preparing
stock-*dipping-+adding medicine liquid->steaming--+washing pulp--)'first
grinding-asecond grinding--+first bleaching~second bleaching--+third
bleaching--> second washing--> removing residue-->recovering
alkali--+treating water-> screening purifying-+pulping, leading to a vast
investment on the equipment of the traditional technology.
For more than 30 years, the patents applied in various countries have
-6-
CA 02654698 2008-12-08
amounted to several tens to lessen the pollution of the paper making
industry, such as the prescription and technology of pulp multistage
bleaching alkali-treatment mongline state oxygen intensified bleach
invented by Nanjing Forest University, China and disclosed in
CN1142555A on February 12, 1997, the method which uses ozone and
chlorine dioxide to bleach pulp invented by France Liquid Air Company
and disclosed in CN1212310A on March 31, 1999, the double reactor
oxygen delignification technology invented by Sweden Gruvon Factory in
Autumn of 1999, the method that uses activated ozone in bleaching pulp
lo invented by Prasel Technique Company, America and disclosed in
CN1297085A on May 30, 2001, the method that uses corn stalk and other
non-wood fiber materials to make pulp invented by America State
University of Northern Carolina and disclosed in CN1371439A on
September 25, 2002, DE10126988A1 disclosed on December 12, 2002,
and the system and device for preparing pulp with wood as the stock
invented by Ooyoi of Japan Company and disclosed in CN1407172A on
April 2, 2003, a pulp-preparing method without pollution invented by
Shandong Changwei Normal School disclosed by China in CN1198492, an
alkali-free pulp-preparing method disclosed in CN1229155, a
polyoxometalate electrochemical bleaching process disclosed in
CN1458075, the basic hydrogen peroxide chemical mechanical pulp
preparing method invented by Shandong Huatai Group Company disclosed
in CN1554827 on December 15, 2004, the method for producing chemical
wood pulp disclosed in CN1563564 on January 12, 2005, the clean
pulp-preparing catalyst and its application invented by Cheng Xiangwu
disclosed in CN1611673 on May 4, 2005, a method of preparing bleached
chemical pulp from cotton stalk disclosed in CN1718919 on January 11,
2006, the pulp clean bleaching method disclosed in CN1737255 on
February 22, 2006, etc..
It is noted after careful reading of all of the above patents that some
of them use non-chlorine bleaching; some reduce the amount of alkali,
chlorine, and sulfur; some replace chlorine with ozone; some use caustic
-7-
CA 02654698 2008-12-08
soda, anthraquinone , and peroxoacid, and some merely make an
improvement on the technological flow. By April 30, 2006, there was no
any enterprise in the world that did not use acids, alkali, chlorine, sulfur,
and anthraquinone to carry out delignification and there was no any
enterprise in the world that had thoroughly banned the pulp-preparing
technology using acids, alkali, chlorine, sulfur, and anthraquinone. In
order to eradicate the pollution caused by the paper making industry from
the headstream, it is necessary to get rid of the theoretical astriction that
says "pulp can not be made without alkali" and find a new pulping theory.
German scientists K. Freudenberg et al came to a conclusion on the
basis of plant chemistry and plant anatomy that lignin comes from its
mother substance, which exists in a form of glucoside of bulk propane.
Such a lignin mother substance liberates glucose under the action of
enzymes, and the remaining coniferal, etc form a viscous substance
depositing on the interlayer between the cell wall and the cell via
polymerization. This viscous substance is lignin.
The polymerization reaction among the lignin structural units is
accomplished mainly by the formation of free radicals, which combine
each other to form dimeric methylenequinone structure, followed by the
addition reaction of H20, lignin structural units, saccaride, etc to
methlenequinone. Namely, the lignin structural units first be
dehydrogenated under the action of hydrogen peroxide and peroxidase
which are formed on the wall of cells and form phenol free radicals and
their resonators, and these free radicals combine with each other to form
dimers. These dimers further dehydrogenate to become free radicals and
combine with other free radicals, carrying out addition reaction between
water and lignin structural units repeatedly and converting lignin to
macromolecules.
-8-
CA 02654698 2008-12-08
~ CH~H CH2OH CH2OH CH2OH CH2OH CH2OH
I1 CH = CH CH ~H CH
CH CH CH CH CH
6 2 -e, H+ =
+- 3 OCH3 OCH3 OCH3 OCH3 OCH3 OCH3
OH 0 O O 0 0
1 II III IV V
CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH
CH CH CH CH CH CH
1i u i 11 11 ii
CH CH CH CH CH CH
6 2 -e, - H+ = -43 OCH3 OCH3 OCH3 OCH3 OCH3
OH O O O O 0
I II IIf IV V
Compared to the biosynthetic course of other natural macromolecular
compounds, the extruding character of the biosynthetic course of lignin is
that once free radicals form, they have nothing to do with the action of
enzyme in the last stage and can arbitrarily combine with each other to
form lignin macromolecules. As we know that a chemical reaction has
reversibility, knowing the upstream of biosynthesis of lignin, it is
understandable that degradation or chain graft of lignin macromolecules
using the free radical theory is the optimum technology.
Therefore, only by creating a new pulping method which does not use
acids, alkali, chlorine, sulfur, and anthraquinone for delignification from
the upstream, can the severe environment pollution problem of the paper
making industry be solved. The present invention just aims at solving the
above problems.
Summary of the invention
On one hand, the present invention provides a method of preparing
2o bleached pulp with high yield by free radical clean pulping process, which
-9-
CA 02654698 2008-12-08
includes the following steps: adding an organic solvent to an
electrochemical vessel containing reactants and water, allowing the pH
value of the reactive medium in said electrochemical vessel to be subacid,
providing electrons by the electrodes to the reactive medium contained in
said electrochemical vessel, introducing oxygen and/or nitrogen into said
electrochemical vessel, whereto a chelating agent, cellulose protectant, and
free radical stabilizing agent are also added to generate various free
radicals and separate lignin from said reactants, thus yielding bleached
pulp.
According to one preferred embodiment of the present invention, the
concentrations of nitrogen and oxygen in said reactive medium are 1-15
mg/m3, respectively.
According to another preferred embodiment of the present invention,
the pH value of said reactive medium is between 3 and 6_9, preferably
between 3.8 and 5.8.
According to another preferred embodiment of the present invention,
the organic solvents is selected from the group consisting of dimethyl
sulfoxide, acetic acid, ethyl acetate, ethyl ether, peracetic acid, benzoyl
peroxide, nitric acid, oxalic acid, and mixtures of two or more of them.
According to another preferred embodiment of the present invention,
the free radical stabilizer is selected from the group consisting of ethylene
oxides, dimethyldioxirane, acetones and ethanols. FRS, Na4P2O7, Na5P3O1a,
3MgO=4SiO2=H2O, H2Si2O5, Mg2' , and DMD are particularly preferred.
According to another preferred embodiment of the present invention,
the free radical is selected from the group consisting of superoxide anion
free radical (0, ), protonized superoxide anion free radical (HOO-),
hydroxyl free radical (-OH), nitroxide free radicals (NO-, N02=), methyl
free radical (=CH3), quinone free radicals (=Q), alkane free radicals (-R),
alkoxy free radicals (LO=) and ester free radicals (LOO-).
According to another preferred embodiment of the present invention,
the reactants come from coniferous woods, hardwoods, grass family stalk
fiber, bast fiber, leaf fiber, or seed coat fiber.
-10-
CA 02654698 2008-12-08
According to another preferred embodiment of the present invention,
the cellulose protectant is selected from the group consisting of
magnesium sulfate, magnesium carbonate, magnesium oxide, sodium
pyrophosphate, sodium dihydrogen phosphate, and mixtures of two or
more of them.
According to another preferred embodiment of the present invention,
the chelating agent is selected from the group consisting of divinyl
triamine pentacetic acid (DTPA), ethylene diamine tetraacetic acid
(EDTA), sodium citrate, opal, zeolite, sodium tripolyphosphate,
io polyoxoethylene alkyl ether, and mixtures of two or more of them. Opal or
sodium tripolyphosphate is particularly preferred.
On the other hand, the present invention provides bleached pulp
obtained by the above method.
Setting out from the nature of biosynthesis of lignin, the present
inventor has invented a pulp-preparing method using free radicals.
Experiments have proved that protonized superoxide free radical (HOO=)
does not damage carbohydrates-cellulose under subacid conditions, thus
significantly inereacing the yield of pulp. The success of these experiments
has brought about a new concept to the paper making industry, and thus
made it to be history that "pulp can not be made without alkali", broken
the three workshop sections of the steaming ball, bleaching tower, and
alkali recovery, and made bleached pulp in an integrated
removing/bleaching electric reaction vessel at one blow. Examination
made by the related national sectors shows that the discharged industrial
waste water in the method of the present invention attains zero pollution,
and the CODc, is lowered by 60-90 times compared to the traditional
chemical pulp process, wherein this value is 140-180 thousand mg/L.
Besides, in the method of the present invention, 80% of water can be
self-recycled for reuse; electricity can be saved by 40%; and the
investment can be saved by 40-50%. Thus the present invention has
radically cured the pollution and solved the urgency of lacking stock,
severe pollution, and great environment protection pressure resulted from
-11-
CA 02654698 2008-12-08
the paper making industry due to the lagging technology.
Embodiments
The present invention discloses a method of preparing pulp with high
yield by free radical clean pulping process, wherein oxygen (02) receives
electrons in an electrochemical vessel in the presence of organic solvent to
form the first superoxide anion free radical (OZ ) with oxygen as the central
atom. The free radical has special physicochemical properties and can
form free radicals of various groups under different reactive conditions. In
water, the free radical is considered to be an alkali, and it forms protonized
superoxide anion free radical (HOO=) by receiving a H}, which is a
conjugating acid of 0.. The water equilibrium value PK is 4.8 and the
concentrations of OZ /HOO- can vary by changing pH value. The
traditional pulp-preparing method obtains O Z from damaged cellulose in
the presence of alkali, because there are significant differences between
OZ and HOO=. Oi is a negatively charged hydrophilic group, which can
not penetrate the middle lamella of the cell and is a kind of reducer under
many circumstances, while HOO- is a neutral hydrophobic group, which
can penetrate the middle lamella of the cell and accumulate in the
hydrophobic region as a strong oxidizer. It can rupture the big n bond in
the benzene ring and side chains of lignin, and degrade and dissolve lignin,
which is further oxidized to be colorless dicarboxylic acid and dissolved,
yielding cellulose with high whiteness. The carbohydrate-cellulose will not
be damaged under subacid conditions. Disproportionation takes place
when two free radicals encounter. For example, in the presence of free
radical stabilizers such as FRS, Na4P207, Na5P3010, 3MgO-4SiO2=H20,
H2 Si2O5, Mg2 1, and DMD, the electron donors will speed up the electron
transfer by 10-40 times due to the conduction of metal ions. The faster the
electron transfer is, the higher the yield of free radicals is and the more
stable of free radicals are.
The mechanisms of the formation of free radicals after reactive
medium obtains electrons, and the reaction among free radicals, benzene
-12-
CA 02654698 2008-12-08
ring, and chromophore, are as follows:
+e H+
02 ---~ 02. --------- 0- HOO=
+e
2H20 =---r- H2O+ + H20= +2e
H20=-~---~ H * + +OH
H20+ + H20 -=-~=- H3O} + =OH
=OH +H202 ------- HOO= + H20
020 + H202 -~;- 02 + OH + 40H
02 + 03 -----~ 02 + 03:
030 + H.+ r------~- HO3=
N2 + 02 +e ~- 2N0=
p 0-0* + H+
+e H+
02 --~----> 02. --=---~.- H00=
+e
2H20 -=,- H2O+ + H20= +2e
HZO= -~- H = + 'OH
-13-
CA 02654698 2008-12-08
H20+ + H20 --~- H30+ + =OH
=OH +H202 ---- ~ HOp. + H20
02= + H202 =-- OZ + OH + .OH
02= + 03 --,, 02 + 03=
03: + H+ --;- H03=
N2 + p2 +e ~- 2N0 =
0- _ / \ O= +H+
Reactions can take place among the above various free radicals to
form new reactive mediums and free radicals. Simultaneously,
spontaneous disproportionation can take place among free radicals, such
as,
e
H+
01 + 02 -----~ H2O2 + 02
The mechanism of delignification of free radicals (with HOO= as an
example) is as follows:
~................,
...............,................c.....,........................................
,..........,:~.,....,..........,,.:..-
...~:..,,........~.,w.,..,,......,,...:.....,,...,..:..,.....,.,..a'r..:.:,:..:
..,.........,...,.....,..;.:y
r `",. ~f3 M 3
~a
NvI..,
{.
5 G~~: ~b~~ >t ;5
~ F ~a!=$ ~.
V
OH
~ ~.~~~:`=~~ ~=~~~..J Ã
-14-
= CA 02654698 2008-12-08
Reaction mechanism of removing non-phenol lignin using protonized
superoxide anion free radicals under subacid conditions
Electrodes used in the present invention can be conventional
electrodes familiar to the one skilled in the art. Particularly preferred
electrodes are nanometer activated carbon electrodes, enzyme electrodes,
mercury electrodes, rare earth electrodes, macromolecular electrodes,
heteropolyoxometalate electrodes, composite electrodes of nickel, titanium,
neodymium, lithium, platinum, cobalt, bismuth, and lead, etc.
Free radical stabilizers used in the present invention refer to
substances which can stabilize free radicals generated in the reaction, for
example, but is not limited to alkylene oxide (FRS), dimethyldioxirane,
acetones and ethanols. FRS, Na4P2O7, Na5P3O10, 3MgO=4SiO2=H20,
H2Si2O5, Mg2 -, DMD, etc are particularly preferred.
Cellulose protectants used in the present invention refer to substances
which can protect cellulose from being damaged during reaction, for
example but is not limited to magnesium sulfate, magnesium carbonate,
magnesium oxide, sodium pyrophosphate, sodium dihydrogen phosphate,
and mixtures of two or more of them. Magnesium carbonate is particularly
preferred.
Chelating agents used in the present invention are divinyl triamine
pentaacetic acid (DTPA), ethylene diamine tetraacetic acid (EDTA),
sodium citrate, opal, zeolite, sodium tripolyphosphate, polyoxoethylene
alkyl ether, and mixtures of two or more of them. Opal and sodium
tripolyphosphate are particularly preferred.
Reactive mediums used in the present invention refer to mediums
which involve in the reaction in the reaction vessel, e.g., it can include
water, organic solvents, free radical stabilizers, reactants (stocks for
pulping), etc.
Organic solvents used in the present invention refer to liquid organic
substances, for example, but is not limited to dimethyl sulfoxide, acetic
acid, ethyl acetate, ethyl ether, peracetic acid, benzoyl peroxide, nitric
acid,
-15-
CA 02654698 2008-12-08
oxalic acid, and mixtures of two or more of them.
Reactants used in the present invention refer to fiber-containing
biological fibers to be bleached and may come from e.g., coniferous woods
(spruce, Chinese red pine, larch, etc), hardwoods (poplar wood, eucalyptus
wood, willow wood, morus wood, etc), grass family stalk fiber (rice stalk,
wheat stalk, bulrush, bamboo, etc), bast fiber (hemp, Abaca, pineapple
fiber, etc), leaf fiber (Eulaliopsis binata, pineapple leaf), and seed coat
fiber (cotton, cotton short-staple, etc).
Subacid conditions used the present invention refer to a pH value
between 3 and 6.9, preferably between 3.8 and 5.8.
Holocelluloses used in the present invention refer to fibers and
hemicelluloses as stocks.
According to one embodiment of the present invention, the method
includes the following steps: preparing stock, rubbing devillicating,
washing, pretreating; feeding the material into an electrochemical vessel
by a screw conveyer, turning on the power of the vessel; introducing
nitrogen into the vessel for 5 min, and introducing oxygen for 10-25 min to
allow the concentration of nitrogen and oxygen in reactive medium to
reach 1-15 mg/m3; adding cellulose protectant, chelating agent, free radical
stabilizer; the total reaction time of free radicals with stocks is 40-60 min;
discharging the material by spray and separating pulp from gas; carrying
out conventional finely-grinding for pulp-preparing, residue removing,
latency, screening, pulping; the waste water from all the procedures is
introduced into the waste water treating system, which can be recycled
after treatment.
Said preparing stock and rubbing devillicating mean feeding the stock,
which is sliced in a conventional slicer (the length and thickness of the slip
are 18-25 mm and 3-6 mm, respectively) and washed, into a rubbing
devillicating machine, wherein it is rubbed into a velour and then fed into
a preheating and impregnating vessel. The pretreating conditions are:
pressure of 0.3 MPa, temperature of 60-80 C , and pH value of 3.8-5.8.
Acids for adjusting the pH value are prepared oxalic acid, nitric acid,
-16-
CA 02654698 2008-12-08
peracetic acid, etc, and the amount thereof is such that the pH value is
subacid. The impregnation time is 15-30 min. The material enters the next
procedure after dehydration.
The materials from the previous procedure are fed into the
electrochemical vessel by a screw conveyer, and the anode in the vessel is
connected to the power source outside the vessel and discharges. Water,
organic solvent and materials in water are reactive mediums and the vessel
wall serves as cathode.
The nitrogen stop being introduced after 5 min, then oxygen is
introduced, and the concentration of nitrogen and oxygen in the reactive
medium is 1-15 mg/m3. Free radical stabilizer is introduced under the same
pressure. When the reaction temperature reaches 140 C, H202 is introduced
by a pressure pump and Mg2 'and Na5P3O10 are introduced simultaneously
as the stabilizer of H202. The reaction conditions of the first reaction are:
1s after introducing nitrogen and oxygen, the temperature is 90-120 C, the
pressure is 0.3-0.6 MPa, and the pH value is 3.8-4.8. The reaction
conditions of the second reaction are: the oxygen pressure is 0.8-1.2 MPa
and the introducing time is 15-20 min, and the pressure in the vessel is
increased to be 0.8-1.2 MPa.
The test results of the pulp prepared by free radical clean pulping
precess
The test of the pilot-plant products made by once reaction in the free
radical electrochemical vessel, a mixed pulp of Eulaliopsis binata (30%)
and wheat stalk (70%), cotton stalk bleached pulp, poplar wood bleached
pulp, etc, was entrusted to authoritative organizations, The State Paper
Quality Supervision and Test Center, Tianjin Science and Technology
University, etc, and the detailed results are shown in the test report. The
test data demonstrate that the oxidation pulping method is applicable not
only to wood, but also to non-wood materials such as agricultural wastes
such as whole cotton stalk, wheat stalk, etc, which are all usable pulping
stocks.
-17-
CA 02654698 2008-12-08
The comparative table of the test reports provided by The State Paper
Quality Supervision and Test Center and Tianjin Science and Technology
University from 2004 to 2005 and the bleached sulfite chemical wood pulp
is as follows:
CID ~ r~ 0 ~
Oo Oo (D a F~
'4)
CD
~ ~ CD ~u ru CD o
~ ` CD
p, cw-, R I~ p. ~ ~.
`D
= ~. ,~ ,--. .~ --= ,--.
UIQ
~
~3
X a ro CD
(D
p s~ ~, A.
CD CD zr,
,'
~ CD CD .o
CD ea
Fiber length 0.50 / / 0.58 0.75
{ Wt average, mm )
Beating degree 45 45 50
( SR )
Qualitification 60 61.5 49.5 61.3 60,0
( g/m2 )
Compactness 3.3 0.54 0.63 0.56
( g/cm3 )
Breaking length 3.2 4.93 4.610 4.049
(Krn)
Tensile index 28.0 46.6 60.3 30.0
( N=m/g )
Tearing index 2.50 3.89 4.88 4.99 3.79
( mNm2/g )
Burst index 1.50 2.10 2.5 3.06 1.13
( KPam2/g )
Whiteness 82.0 82.6 83.3 79 76
(%1S0)
Opacity 88.1 80.2 80.02 82.82
(%)
-18-
CA 02654698 2008-12-08
The present invention provides a method of preparing bleached pulp
with high yield by free radical clean process, the stocks of which are
coniferous woods (spruce, Chinese red pine, larch, etc), hardwoods (poplar
wood, eucalyptus wood, willow wood, morus wood, etc), grass family
stalk fiber (rice stalk, wheat stalk, bulrush, bamboo, etc), bast fiber (hemp,
Abaca, pineapple fiber, etc), leaf fiber (Eulaliopsis binata, pineapple leaf),
seed coat fiber (cotton, cotton short-staple, etc), and whole cotton stalk,
which is similar to but is not wood.
More detailed description of the present invention will be given
below in combination with examples.
Example 1
100 g spruce sheets (absolutely dry amount) were rubbed into velour
using a rubbing devillicating machine and the impurity was removed by
wind power. After purifying with 60 C recycled hot water, the material was
introduced into a preheating impregnator by a conveyer apron and
pretreated under a pressure of 0.3 MPa and a pH value of 4.8 at 80 C for
30 min. After dehydration, the material was introduced by a screw
conveyer into an electrochemical vessel (M-O-P-III model, made by
Tianjin Light Industry Machinery Plant), wherein electrons were
continuously generated under a linear stirring rotating speed of 0.8-1.2 m/s,
a temperature of 140 C, and a pH value of 3.8 using the conventional
electrode. After introducing nitrogen for 5 min, the oxygen was introduced,
allowing the concentration of nitrogen and oxygen in the reactive medium
(including water, oxalic acid, and the stocks) to reach 1-15 mg/m3. 0.008 g
magnesium oxide as the cellulose protectant, 0.002 g EDTA as the
chelating agent, and 0.15 g Na5P3O10 as the free radical stabilizer were
added under a pressure of 0.3 MPa, then the valve was turned off. The
pressure was raised to 0.8 MPa and the reaction was conducted for 45 min.
After the reaction was conducted at the constant pressure for 10 min, the
pressure was lowered to 0.15 MPa. The discharge valve was turned on and
the reactive medium entered the spray pulp-gas separation and dehydration
-19-
CA 02654698 2008-12-08
unit. The vent valve was turned on to discharge the hot gas to the recycle
water box, and the hot gas was subjected to recycle treatment for reuse.
The pulp was repeatedly washed twice in a screw pulp-washer with 60 C
deionized water, yielding a bleached pulp ISO with a whiteness of 68-78%
after dehydration, fine grinding, node removal, and latency. This whiteness
was the reaction whiteness after once integrated discoloration and bleach.
The yield of the holocellulose was 62-75 %.
Example 2
Example 2 was the same as example I but the difference was that the
stock was larch sheets. The sheets were rubbed into velour using a rubbing
devillicating machine and the impurity was removed by wind power. After
purifying with 60 C recycled hot water, the material was introduced into a
preheating impregnator by a conveyer apron. After dehydration, the
1s material was introduced by a screw conveyer into an electrochemical
vessel, wherein electrons were continuously generated under a linear
stirring rotating speed of 0. 8-1.2 m/s, a temperature of 120 C , and a pH
value of 3.9 using the conventional electrode. After introducing nitrogen
for 5 min, the oxygen was introduced, allowing the concentration of
2o nitrogen and oxygen in the reactive medium (including water, peracetic
acid, and the material) to reach 1-15 mg/m3. 0.005 g magnesium carbonate
as the cellulose protectant, 0.0015 g DTPA as the chelating agent, and 0.1
g FRS as the free radical stabilizer were added under a pressure of 0.4
MPa and the valve was turned off. The pressure was raised to 0.8 MPa and
25 the reaction was conducted for 30 min. After the reaction was conducted at
constant pressure for 10 min, the pressure was lowered to 0.15 MPa. The
discharge valve was turned on and the reactive medium entered the spray
pulp-gas separation and dehydration unit. The vent valve was turned on to
discharge the hot gas to the recycle water box, and the hot gas was
30 subjected to cyclic treatment for reuse. The pulp was repeatedly washed
twice in a screw pulp-washer with 60 C deionized water, yielding a
bleached pulp ISO with a whiteness of 68-76% after dehydration, fine
-20-
CA 02654698 2008-12-08
grinding, node removal, and latency. This whiteness was the reaction
whiteness after once integrated discoloration and bleach. The yield of the
holocellulose was 65-78 % .
Example 3
Example 3 was the same as example I but the difference was that the
stock was poplar wood sheets. The sheets were rubbed into velour using a
rubbing devillicating machine and the impurity was removed by wind
power. After purifying with 60 C recycled hot water, the material was
introduced into a preheating impregnator by a conveyer apron. After
dehydration, the material was introduced by a screw conveyer into an
electrochemical vessel, wherein electrons were continuously generated
under a linear stirring rotating speed of 0.8-1.2 m/s, a temperature of
140 C, and a pH value of 4.0 using the conventional electrode. After
introducing nitrogen for 5 min, oxygen was introduced, allowing the
concentration of nitrogen and oxygen in the reactive medium (including
water, acetic acid, and the material) to attain 1-15 mg/m3. 0.007 g
magnesium oxide as the cellulose protectant, 0.002 g sodium citrate as the
chelating agent, and 0.12 g DMD as the free radical stabilizer were added
under a pressure of 0.4 MPa and the valve was turned off. The pressure
was raised to 0.8 MPa and the reaction was conducted for 30 min. After
the reaction was conducted at constant pressure for 10 min, the pressure
was lowered to 0.15 MPa. The discharge valve was turned on and the
reactive medium entered the spray pulp-gas separation and dehydration
unit. The vent valve was turned on to discharge the hot gas to the recycle
water box, and the hot gas was subjected to cyclic treatment for reuse. The
pulp was repeatedly washed twice in a screw pulp-washer with 60'C
deionized water, yielding a bleached pulp ISO with a whiteness of
76-84.5% after dehydration, fine grinding, node removal, and latency. This
whiteness was the reaction whiteness after once integrated discoloration
and bleach. The yield of the holocellulose was 60-76 %.
-21-
CA 02654698 2008-12-08
Example 4
Example 4 was the same as example I but the difference was that the
stock was whole cotton stalk. The sheets were rubbed into velour using a
rubbing devillicating machine and the impurity was removed by wind
power. After purifying with 60 C recycled hot water, the material was
introduced into a preheating impregnator by a conveyer apron. After
dehydration, the material was introduced by a screw conveyer into an
electrochemical vessel, wherein electrons were continuously generated
under a linear stirring rotating speed of 0.8-1.2 m/s, a temperature of
lo 130 C, and a pH value of 4.8 using the conventional electrode. After
introducing nitrogen for 5 min, oxygen was introduced, allowing the
concentration of nitrogen and oxygen in the reactive medium (including
water, acetic acid, and the material) to attain 1-15 mg/m3. 0.005 g sodium
dihydrogen phosphate as the cellulose protectant, 0.002 g zeolite as the
chelating agent, and 0.1. g H2Si2Os as the free radical stabilizer were added
under a pressure of 0.4 MPa and the valve was turned off. The pressure
was raised to 0.8 MPa and the reaction was conducted for 40 min. After
the reaction was conducted at constant pressure for 10 min, the pressure
was lowered to 0.15 MPa. The discharge valve was turned on and the
reactive medium entered the spray pulp-gas separation and dehydration
unit. The vent valve was turned on to discharge the hot gas to the recycle
water box, and the hot gas was subjected to cyclic treatment for reuse. The
pulp was repeatedly washed twice in a screw pulp-washer with 60 C
deionized water, yielding a bleached pulp ISO with a whiteness of 72-79%
after dehydration, fine grinding, node removal, and latency. This whiteness
was the reaction whiteness after once integrated discoloration and bleach.
The yield of the holocellulose was 68-77 %.
Example 5
100 g rice stalk (absolutely dry amount) were rubbed into velour
using a rubbing devillicating machine and the impurity was removed by
wind power. After purifying with 60 C recycled hot water, the material was
-22-
= , CA 02654698 2008-12-08
introduced into a preheating impregnator by a conveyer apron and
pretreated under the pressure of 0.3 MPa and pH value of 4.8 at 80 C for
30 min.. After dehydration, the material was introduced by a screw
conveyer into an electrochemical vessel, wherein electrons were
continuously generated under a linear stirring rotating speed of 0.8-1.2 m/s,
a temperature of 140 C, and a pH value of 3.8 using the conventional
electrode. After introducing nitrogen for 5 min, oxygen was introduced,
allowing the concentration of nitrogen and oxygen in the reactive medium
(including water, peracetic acid, and the material) to attain 1-15 mg/m3.
lo 0.008 g magnesium sulfate as the cellulose protectant, 0.002 g opal as the
chelating agent, and 0.15 g 3MgO=4SiO2-H2O as the free radical stabilizer
were added under a pressure of 0.3 MPa and the valve was turned off. The
pressure was raised to 0.8 MPa and the reaction was conducted for 45 min.
After the reaction was conducted at constant pressure for 10 min, the
pressure was lowered to 0.15 MPa. The discharge valve was turned on and
the reactive medium entered the spray pulp-gas separation and dehydration
unit. The vent valve was turned on to discharge the hot gas to the recycle
water box, and the hot gas was subjected to cyclic treatment for reuse. The
pulp was repeatedly washed twice in a screw pulp-washer with 60 C
deionized water, yielding a bleached pulp ISO with a whiteness of 68-75%
after dehydration, fine grinding, node removal, and latency. This whiteness
was the reaction whiteness after once integrated discoloration and bleach.
The yield of the holocellulose was 52-68 %.
Example 6
Example 6 was the same as example 5 but the difference was that the
stock was wheat stalk, yielding a bleached pulp ISO with a whiteness of
70-82%. This whiteness was the reaction whiteness after once integrated
discoloration and bleach. The yield of the holocellulose was 55-70 %.
Example 7
Example 7 was the same as example 5 but the difference was that the
- 23 -
r =
CA 02654698 2008-12-08
stock was Abaca. It was rubbed into velour using a rubbing devillicating
machine and the impurity was removed by wind power. After purifying
with 60 C recycled hot water, the material was introduced into a
preheating impregnator by a conveyer apron. After dehydration, the
material was introduced by a screw conveyer into an electrochemical
vessel, wherein electrons were continuously generated under a linear
stirring rotating speed of 0.8-1.2 m/s, a temperature of 140 C, and a pH
value of 4.0 using the conventional electrode. After introducing nitrogen
for 5 min, oxygen was introduced, allowing the concentration of nitrogen
1o and oxygen in the reactive medium (including water, dimethyl sulfoxide,
and the material) to attain 1-15 mg/m3. 0.007 g sodium pyrophosphate as
the cellulose protectant, 0.002 g tripolyphosphate as the chelating agent,
and 0.12 g Na4P2O7 as the free radical stabilizer were added under a
pressure of 0.4 MPa and the valve was turned off. The pressure was raised
to 0.8 MPa and the reaction was conducted for 30 min. After the reaction
was conducted at constant pressure for 10 min, the pressure was lowered to
0.15 MPa. The discharge valve was turned on and the reactive medium
entered the spray pulp-gas separation and dehydration unit. The vent valve
was turned on to discharge the hot gas to the recycle water box, and the hot
gas was subjected to cyclic treatment for reuse. The pulp was repeatedly
washed twice in a screw pulp-washer with 60 C deionized water, yielding
a bleached pulp ISO with a whiteness of 78-86% after dehydration, fine
grinding, node removal, and latency. This whiteness was the reaction
whiteness after once integrated discoloration and bleach. The yield of the
holocellulose was 60-72 % .
Example 8
Example 8 was the same as example 5 but the difference was that the
stock was Eulaliopsis binata. It was rubbed into velour using a rubbing
3o devillicating machine and the impurity was removed by wind power. After
purifying with 60 C recycled hot water, the material was introduced into a
preheating impregnator by a conveyer apron. After dehydration, the
- 24 -
r t
CA 02654698 2008-12-08
.,
material was introduced by a screw conveyer into an electrochemical
vessel, wherein electrons were continuously generated under a linear
stirring rotating speed of 0.8-1.2 m/s, a temperature of 130 C, and a pH
value of 4.8 using the conventional electrode. After introducing nitrogen
for 5 min, oxygen was introduced, allowing the concentration of nitrogen
and oxygen in the reactive medium (including water, ethyl acetate, and the
material) to attain 1-15 mg/m3. 0.005 g magnesium phosphate as the
cellulose protectant, 0.002 g zeolite as the chelating agent, and 0.1 g
Na4P2O7 as the free radical stabilizer were added under a pressure of 0.4
MPa and the valve was turned off. The pressure was raised to 0.8 MPa and
the reaction was conducted for 40 min. After the reaction was conducted at
constant pressure for 10 min, the pressure was lowered to 0.15 MPa. The
discharge valve was turned on and the reactive medium entered the spray
pulp-gas separation and dehydration unit. The vent valve was turned on to
discharge the hot gas to the recycle water box, and the hot gas was
subjected to cyclic treatment for reuse. The pulp was repeatedly washed
twice in a screw pulp-washer with 60 C deionized water, yielding a
bleached pulp ISO with a whiteness of 74-83% after dehydration, fine
grinding, node removal, and latency. This whiteness was the reaction
whiteness after once integrated discoloration and bleach. The yield of the
holocellulose was 68-79 % .
- 25 -
