U.S. patent application number 09/371343 was filed with the patent office on 2002-07-04 for method for producing cellulose derivatives.
This patent application is currently assigned to Novozymes A/S. Invention is credited to KAMACHI, MOTOAKI, NOGUCHI, YOSHITAKA.
Application Number | 20020084047 09/371343 |
Document ID | / |
Family ID | 8155989 |
Filed Date | 2002-07-04 |
United States Patent
Application |
20020084047 |
Kind Code |
A1 |
NOGUCHI, YOSHITAKA ; et
al. |
July 4, 2002 |
METHOD FOR PRODUCING CELLULOSE DERIVATIVES
Abstract
Pulp is treated with a hemicellulase, e.g. a xylanase such as
that derived from Bacillus sp. SD902, prior to being chemically
modified. This results in excellent cellulose derivatives that
could not be obtained by any conventional methods. Specifically,
the cellulose derivatives produced by this method have improved
filterability and increased water-solubility. In addition,
according to this method, the formation of microgel is minimized,
and the distribution of the substituents in the cellulose
derivatives through the intramolecular substitution in the method
is made more uniform.
Inventors: |
NOGUCHI, YOSHITAKA;
(MINATO-KU, JP) ; KAMACHI, MOTOAKI; (AMHERST,
MA) |
Correspondence
Address: |
NOVOZYMES NORTH AMERICA, INC.
C/O NOVO NORDISK OF NORTH AMERICA, INC.
405 LEXINGTON AVENUE, SUITE 6400
NEW YORK
NY
10174
US
|
Assignee: |
Novozymes A/S
Bagsvaerd
DK
|
Family ID: |
8155989 |
Appl. No.: |
09/371343 |
Filed: |
August 10, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09371343 |
Aug 10, 1999 |
|
|
|
PCT/DK97/00089 |
Feb 28, 1997 |
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Current U.S.
Class: |
162/72 ; 435/277;
435/278 |
Current CPC
Class: |
C08B 11/12 20130101;
D21C 9/002 20130101; C08B 11/02 20130101; C08B 11/00 20130101 |
Class at
Publication: |
162/72 ; 435/277;
435/278 |
International
Class: |
D21C 003/20 |
Claims
1. A method for producing a cellulose derivative, which comprises
a)treating the pulp with a hemicellulase, and b)chemically
modifying the treated pulp.
2. The method of claim 1, wherein the hemicellulase is an enzyme
that hydrolyzes .beta.-1,4-glycoside bonds.
3. The method of claim 1, wherein the hemicellulase is a
xylanase.
4. The method of claim 1, wherein the xylanase is obtainable from
Bacillus sp. SD902.
5. The method of claim 1, wherein the chemical modification is
etherification.
6. The method of any of claim 1, wherein the chemical modification
is methyl-etherification, ethyl-etherification,
hydroxyethyl-etherification, hydroxypropyl-etherification, or
carboxymethyl-etherification.
Description
INDUSTRIAL FIELD
[0001] The present invention relates to a method for producing
cellulose derivatives. More specifically, it relates to a method
for producing cellulose derivatives from enzymatically-treated
cellulose.
BACKGROUND ART
[0002] Cellulose derivatives include cellulose ethers. Cellulose
ethers, such as methyl cellulose (MC), ethyl cellulose (EC)
hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC) and
carboxymethyl cellulose (CMC), are water-soluble or
water-suspensible white polymers which are non-caloric, odorless
and tasteless. Therefore, such cellulose ethers are widely used in
various fields, for example, foods, chemicals, cosmetics,
paper-making and fibers, as thickeners, binders, stabilizers,
suspending agents etc.
[0003] With the recent development of novel uses, there is a demand
cellulose ethers with high-grade properties that are applicable to
such novel uses. For example, there is a demand for cellulose
ethers giving a reduced amount of microgel. Microgel as referred to
herein is cellulose ether in the form of a semi-dissolved gel which
is not completely solubilized in solvents because the
etherification is incomplete.
[0004] To produce cellulose ethers, a method has heretofore been
employed in which a lignocellulose, such as wood pulp or linter
pulp, is soaked in a strong alkali solution to give an alkali
cellulose, and thereafter the resulting alkali cellulose is treated
with a suitable etherifying agent (e.g., methyl chloride, ethyl
chloride, ethylene oxide, propylene oxide, monochloroacetic
acid).
[0005] The cellulose ethers as produced according to this method
could not always have satisfactory characteristics for some uses,
as the properties are much influenced by the degree of substitution
(degree of etherification) and the distribution of substituents.
For example, cellulose ethers with a low degree of substitution are
poorly soluble in solvents, because of uneven etherification. In
addition, these often give a semi-dissolved gel substance which is
referred to as a microgel. The gel substance, microgel is not only
sensually (visually and tactually) unfavorable but also results in
poor filterability of solutions of the cellulose ethers.
[0006] Enzymatic treatment of pulp has been studied, using
cellulases and xylanases as the enzymes. For example, in 1986,
Viikari et al. reported in Proceedings of the Symposium on
Biotechnology in the Pulp and Paper Industry, 3rd International
Conference, a method of enzymatically pre-treating pulp prior to
bleaching it to thereby reduce the amounts of the chemicals to be
used in the subsequent bleaching step.
[0007] EP 382,576 discloses a method of treating CMC with a
cellulase to produce CMC hydrolysates. However, this method
involves an enzymatic treatment of CMC after the etherification of
pulp, so it does not reduce the amount of microgel during the
etherification step. Accordingly, if the microgel is to be removed,
a large amount of the enzyme must be used, resulting in noticeable
reduction in the yield of the intended hydrolysates. On the other
hand, if the yield of the hydrolysates is to be increased in this
method, the amount of the enzyme to be used therein must be
reduced. However, this is problematic in that the enzymatic
treatment of the microgel is insufficient, resulting in still
leaving a large amount of microgel in the system. In addition,
since the viscosity of the hydrolysates obtained in this method is
much lowered, as compared with that of the original CMC, the
hydrolysates are disadvantageous when used as thickeners or
binders.
[0008] DE 44 40 245 C1 discloses a method of producing
hydroxyalkyl-cellulose ethers by pre-treating cellulose with a
cellulase solution, followed by a treatment with epoxyalkane in the
presence of a quaternary ammonium base. The cellulase treatment
reduced the degree of polymerization. No effect on the filtration
rate is reported.
[0009] Given the situation, the object of the present invention is
to provide cellulose derivatives with improved filterability while
preventing the formation of microgel in the step of producing
cellulose derivatives from pulp.
STATEMENT OF THE INVENTION
[0010] We, the present inventors have assiduously studied in order
to solve the above-mentioned problems in the prior art, and have
found that treating a pulp with a hemicellulase, e.g. a xylanase
such as that derived from Bacillus sp. SD902, prior to chemical
modification results in excellent cellulose derivatives that could
not be obtained by any conventional methods. Specifically, the
cellulose derivatives produced by this method have improved
filterability and increased water-solubility. In addition,
according to this method, the formation of microgel is minimized,
and the intramolecular distribution of substituents in the
cellulose derivative is made more uniform. On the basis of these
findings, we have completed the present invention.
[0011] Accordingly, the invention provides a method for producing a
cellulose derivative, which comprises
[0012] a)treating the pulp with a hemicellulase, and
[0013] b)chemically modifying the treated pulp.
[0014] Now, the present invention is described in detail
hereinunder.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Pulp
[0016] The pulp to be used in the present invention may be steamed
or bleached pulp derived from coniferous trees (softwood),
broad-leaved trees (hardwood) or non-wood plants. The non-wood pulp
may be pulp produced from liber plants, such as kozo (paper
mulberry; Broussonetia kazinoki), mitsumata (Edgeworthia
papyrifera), Manila hemp, kenaf; or from hard fiber plants, such as
straw, sugar cane, bagasse. In addition, cellulose derivatives
having a low degree of chemical modification such as
etherification, and also regenerated celluloses can also be used as
the starting pulp in the present invention.
[0017] Hemicellulase
[0018] The hemicellulase used in this invention is preferably an
enzyme that hydrolyzes .beta.-1,4-glycoside bonds. One enzyme or a
plurality of enzymes may be used. Some preferred types of
hemicellulase are xylanase, mannanase and xylo-glucanase.
[0019] The xylanase may be a xylanolytic enzyme obtained from any
known source of xylanolytic enzymes. Preferably the xylanolytic
enzyme may be obtained from microbial sources, in particular from a
filamentous fungus or yeast, or from a bacteria.
[0020] Preferred xylanolytic enzymes of fungal origin are xylanases
derived from a strain of Aspergillus, in particular A. aculeatus,
A. awamori, A. nidulans, A. niger, A. kawachii, or A. tubigensis,
Aureobasidium, Chaetomium, in particular C. gracile, Cochliobolus,
in particular C. carbonum, Disporotrichum, in particular D.
dimorphosporum, Humicola, in particular H. insolens,
Neocallimastix, in particular N. patriciarum, Orpinomyces,
Penicillium, in particular P. janthinellum, Thermomyces, in
particular T. lanuginosus (syn. Humicola lanuginosa), or
Trichoderma, in particular T. longibrachiatum, or T. reesei.
[0021] Preferred xylanolytic enzymes of bacterial origin are
xylanases derived from a strain of Bacillus, in particular B.
pumilus, B. stearothermophilus, or B. subtilis, Cellulomonas fimi,
in particular C. fimi, Clostridium, in particular C. thermocellum,
Dictyoglomus, in particular D. thermophilum, Microtetraspora, in
particular M. flexuosa, Streptomyces, in particular S.
olivochromogenes, or Thermomonospora.
[0022] A particularly preferred xylanase is derived from Bacillus
sp. SD902; it may be produced by cultivation of the strain and
recovery of the xylanase as described in EP 720,649. The enzyme is
hereinafter referred to as SDX enzyme. Bacillus sp. strain SD902
was deposited for the purposes of patenting at the National
Institute of Bioscience and Human-Technology, Agency of Industrial
Science and Technology, Ministry of International Trade and
Industry, 1-3Higashi 1-chome, Tsukuba-shi, Ibaraki-ken 305, Japan.
It was deposited by Showa Denko K.K. on Dec. 25, 1992 under deposit
No. FERM P-13356, was transferred on Dec. 22, 1993 to international
deposit FERM BP-4508 under the terms of the Budapest Treaty, and
was later assigned to Novo Nordisk A/S.
[0023] The mannanase may be obtained from microbial sources, in
particular from a filamentous fungus or yeast, or from a bacteria.
A preferred mannanase of fungal origin is derived from Trichoderma,
particularly T. reesei. This enzyme may be produced as described in
WO 93/24622.
[0024] The enzyme to be used herein is not always required to be
pure, but any of cell-free supernatants as obtained through
centrifugation of cultures of enzyme-producing cells, or crude
enzyme extracts as extracted from incubated cells may be used.
[0025] The activity of the enzyme for use in the present invention
can be determined by quantifying the reducing sugar as formed
through the enzymatic reaction with its substrate (e.g., xylan in
the case of xylanase), at pH 7 and at 50.degree. C., according to a
method of using 3,5-dinitrosalicylic acid. One unit (U) for the
enzymatic activity indicates the amount of the enzyme that forms 1
.mu.mol of reducing sugar (e.g., xylose in the case of xylanase)
per minute.
[0026] Conditions for Enzyme Treatment
[0027] The conditions for the enzymatic treatment of pulp according
to the invention are not particularly limited. The pH, temperature
and process time for the treatment may be suitably defined in such
a manner that the enzyme being used is kept active within the
defined ranges. Typical conditions are: a temperature between
20.degree. C. and 90.degree. C., preferably between 40.degree. C.
and 80.degree. C.; process time between 15 minutes and 24 hours,
preferably between 30 minutes and 5 hours; and a pH between 3 and
9, preferably between 4 and 8.
[0028] The amount of the enzyme to be added to pulp may be from 1
to 1000 U/g (based on pulp dry matter), preferably from 2 to 250
U/g. If the amount of the enzyme added is smaller than 1 U/g, it
may be too small to attain the intended enzymatic treatment; an
enzyme amount larger than 1000 U/g is not preferred because the
pulp yield may be reduced.
[0029] The concentration of pulp to be in the system may be any one
that ensures satisfactory stirring and mixing of pulp therein, but
is preferably in the range 1-20% by weight.
[0030] Chemical Modification
[0031] The chemical modification that follows the enzymatic
treatment in the method of the present invention is preferably
etherification, more preferably alkyl etherification, hydroxyalkyl
etherification or carboxyalkyl etherification, even more preferably
methyl etherification, ethyl etherification, hydroxyethyl
etherification, hydroxypropyl etherification or carboxymethyl
etherification.
[0032] The method used in the chemical modification of the
enzymatically-treated pulp can be any known method. For example,
CMC, MC, EC, HEC or HPC may be produced from pulp by two typical
methods. One is an aqueous method where an aqueous medium is used
as the reaction solvent; and the other is a solvent method where an
organic solvent is used.
[0033] Examples of aqueous methods for producing CMC are an alkali
cellulose method where pulp is soaked in a solution of sodium
hydroxide, and powdery sodium monochloroacetate is added thereto
while beating and stirring it; and a monochlorine method where pulp
is soaked in an aqueous solution of sodium monochloroacetate, and
sodium hydroxide is added thereto while beating and stirring
it.
[0034] Examples of the solvent method are a 6-fold method that uses
a mixed solvent of ethanol and benzene; and a 30-fold method that
uses an aqueous solution of 2-propanol.
[0035] Apart from such chemical modification, enzymatic
modification may also be used.
EXAMPLES
[0036] Now, the present invention is describe in more detail with
reference to the following examples that are based on experiments.
However, these examples are not intended to restrict the scope of
the invention. In the examples, all percentages indicate % by
weight.
Example 1
[0037] Commercially-available bleached pulp (trade name "ARAUCO")
was made into a 5% slurry with an acetic acid buffer (pH 6), to
which was added SDX enzyme in an amount of 50 U/g (relative to pulp
dry matter). The pulp slurry was enzymatically treated at
60.degree. C. for 3 hours with stirring, and then de-watered by
filtration through a Buchner funnel. The enzymatically-treated pulp
thus obtained was then carboxymethyl-etherifie- d to give CMC,
according to the CM etherification method mentioned below. The
characteristics of the CMC thus obtained herein were compared with
those of non-enzymatically treated CMC.
[0038] Methods for determining the characteristics of CMC samples
are mentioned hereinunder.
[0039] CM Etherification of Pulp
[0040] A slurry was prepared by stirring pulp with 30 times by
weight of 88% isopropanol. Relative to the amount of glucose units,
1.8 mole of sodium hydroxide was added to form alkali cellulose,
followed by 0.8 mole of monochloroacetic acid, and this was reacted
at 70 to 80.degree. C. for 2.5 hours. After the reaction, the
reaction mixture was filtered through a Buchner funnel and washed
with an aqueous solution of 75-80% methanol. This filtration and
washing was repeated several times. Then, the residue was dried to
obtain a pure CMC.
[0041] Filtration Rate
[0042] An aqueous solution of 0.5% CMC sample to be tested was kept
at 20.degree. C. and applied onto a 200-mesh sieve, whereupon the
amount of the filtrate passing through the sieve within 5 minutes
was measured using a measuring cylinder.
[0043] Viscosity
[0044] An aqueous solution of 2% CMC sample to be tested was kept
at 20.degree. C. and subjected to viscosimetry using a single
cylindrical rotational viscosimeter to determine its viscosity.
[0045] Amount of Microgel
[0046] An aqueous solution of 0.5% CMC sample to be tested was kept
at 20.degree. C. and applied onto a 200-mesh sieve, whereupon the
wet weight of gel remaining on the sieve was measured and
represented as % by weight relative to CMC.
1 Enzyme-Treated CMC CMC Filtration Rate (ml/5 30 18 min) Viscosity
(cps) 1400 1260 Amount of Microgel 4.0 20.5 (%)
Example 2
[0047] Pulp was enzymatically treated in the same manner as in
Example 1, and then modified into CMC according to the alkali
cellulose method mentioned below. The characteristics of the CMC
thus obtained herein were compared with those of non-enzymatically
treated CMC.
[0048] Alkali Cellulose Method
[0049] Pulp was soaked in an aqueous solution of 18% sodium
hydroxide. After one or two hours, this was squeezed to remove the
excess sodium hydroxide, thereby obtaining an alkali cellulose of 3
times by weight relative to pulp. The resulting alkali cellulose
was transferred into a beater. Powder sodium monochloroacetate in
an amount of 1.2 to 2.0 mole per mole of anhydrous glucose unit in
the pulp was added while beating and stirring. This was further
beaten and stirred further for several hours, while keeping the
temperature at 10.degree. C. or lower, whereby sodium
monochloroacetate fully penetrated into the cellulose structure.
After this, the resulting mixture was transferred into a reactor,
and kept therein at from 70 to 80.degree. C. for about 2 hours,
with further stirring, to give CMC. The reaction mixture was
filtered and washed several times with an aqueous solution of
75-80% methanol, and the resulting residue was dried to obtain a
pure CMC.
2 Enzyme-Treated CMC CMC Filtration Rate (ml/5 32 25 min) Viscosity
(cps) 2800 2500 Amount of Microgel 4.5 26.1 (%)
Example 3
[0050] Commercially-available bleached pulp (trade name "ARAUCO")
was made into a 15% slurry with phosphoric acid buffer (pH 8), to
which was added SDX enzyme in an amount of 100 U/g (relative to
pulp dry matter). With stirring, the pulp slurry was enzymatically
treated at 70.degree. C. for 5 hours, and then de-watered by
filtration through a Buchner funnel. The enzymatically-treated pulp
thus obtained was then methyl-etherified to give methyl cellulose,
according to the methyl etherification method mentioned below. As a
control, pulp that had not been enzymatically treated was
methyl-etherified. Its characteristics were compared with those of
the enzymatically-treated methyl cellulose.
[0051] Methyl Etherification Method
[0052] Pulp was soaked in a solution of about 50% sodium hydroxide,
and then squeezed to obtain an alkali cellulose having sodium
hydroxide and water in almost the same amount as that of cellulose.
To this was added a slight excess of methyl chloride, and this was
reacted at 95 to 100.degree. C. in an autoclave. After the
reaction, the reaction mixture was washed with hot water on a
Buchner funnel and then dried to obtain pure methyl cellulose.
3 Enzyme-Treated MC MC Filtration Rate 28 20 (ml/5 min) Viscosity
(cps) 1100 980
[0053] Advantages of the Invention
[0054] The method of the present invention produces cellulose
derivatives with better filterability than conventional cellulose
derivatives, while preventing the formation of microgel. The
cellulose derivatives thus obtained in the present invention can be
effectively used, for example, as thickeners, stabilizers and
suspending agents.
[0055] Depending on the enzyme used in the method of the invention,
the characteristics, such as those mentioned above, of cellulose
derivatives obtained may be improved without lowering their
viscosity. Thus, the present invention is especially advantageous
in this respect.
* * * * *