U.S. patent application number 14/401166 was filed with the patent office on 2015-04-23 for method of separation of hemicellulose and cellulose from polysaccharide sources.
This patent application is currently assigned to METSA FIBRE OY. The applicant listed for this patent is METSA FIBRE OY. Invention is credited to Michael Hummel, Mikhail Iakovlev, Herbert Sixta, Lasse Tolonen.
Application Number | 20150107790 14/401166 |
Document ID | / |
Family ID | 48289226 |
Filed Date | 2015-04-23 |
United States Patent
Application |
20150107790 |
Kind Code |
A1 |
Sixta; Herbert ; et
al. |
April 23, 2015 |
METHOD OF SEPARATION OF HEMICELLULOSE AND CELLULOSE FROM
POLYSACCHARIDE SOURCES
Abstract
A method of separating hemicellulose and cellulose by
dissolution of hemicellulose from a hemicellulose-rich source, such
as a pulp of any origin or from holocellulose. In the method,
hemicellulose is dissolved in a solvent system comprising a
cellulose solvent, which is either a ionic liquid or another direct
cellulose solvent, and a molecular solvent (co-solvent), wherein
said co-solvent does not dissolve cellulose, and wherein the
solvent basicity and acidity of said ionic liquid or other direct
cellulose solvent are adequately adjusted by the co-solvent. The
present invention enables quantitative separation of cellulose and
hemicellulose without any depolymerization and yield losses as
occurring during conventional dissolving pulp manufacturing
processes.
Inventors: |
Sixta; Herbert; (Aalto,
FI) ; Hummel; Michael; (Aalto, FI) ; Iakovlev;
Mikhail; (Aalto, FI) ; Tolonen; Lasse; (Aalto,
FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
METSA FIBRE OY |
Metsa |
|
FI |
|
|
Assignee: |
METSA FIBRE OY
Metsa
FI
|
Family ID: |
48289226 |
Appl. No.: |
14/401166 |
Filed: |
April 15, 2013 |
PCT Filed: |
April 15, 2013 |
PCT NO: |
PCT/FI2013/050414 |
371 Date: |
November 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61646383 |
May 14, 2012 |
|
|
|
Current U.S.
Class: |
162/76 |
Current CPC
Class: |
D21H 11/16 20130101;
D21C 9/086 20130101; D21C 9/005 20130101; C08H 8/00 20130101; Y02P
20/54 20151101; C08B 1/003 20130101; Y02P 20/542 20151101; C08B
37/0057 20130101; C08B 37/0003 20130101; D21H 17/14 20130101 |
Class at
Publication: |
162/76 |
International
Class: |
D21H 17/14 20060101
D21H017/14; D21H 11/16 20060101 D21H011/16; D21C 9/08 20060101
D21C009/08 |
Claims
1. A method of separating hemicellulose and cellulose by
dissolution of hemicellulose from a hemicellulose-rich source, such
as a pulp of any origin or from holocellulose, characterized in
that wherein hemicellulose is dissolved in a solvent system
comprising a cellulose solvent, which is either a ionic liquid or
another direct cellulose solvent, and a molecular solvent
(co-solvent), wherein said co-solvent does not dissolve cellulose,
and wherein the solvent basicity and acidity of said ionic liquid
or other direct cellulose solvent are adequately adjusted by the
co-solvent.
2. The method according to claim 1, characterized in that wherein
hemicellulose is dissolved in a solvent system comprising a ionic
liquid and a molecular solvent (co-solvent), wherein said
co-solvent does not dissolve cellulose and wherein the solvent
basicity and acidity of said ionic liquid are adequately adjusted
by the co-solvent.
3. The method according to claim 1, wherein the solvent basicity
and acidity are characterized by the Kamlet-Taft solubility
parameters, particularly by the .beta.- (H-bond basicity) and
.alpha.- (H-bond acidity) values.
4. The method according to claim 1, wherein said co-solvent is
miscible with the ionic liquid.
5. The method according to claim 1, wherein said co-solvent is
capable of lowering the .beta.-value and/or raising the
.alpha.-value of the solvent system.
6. The method according to claim 1, wherein i) the ionic liquid is
a direct cellulose solvent, which preferably has a cation selected
from the group of cationic moieties depicted in FIG. 2, wherein the
residues R.sub.1-5 are independently linear or branched alkyl-
(typically C1-C6), alkoxy-, or alkoxyalkyl groups, residues
containing aryl moieties, or hydrogen, and an anion selected from
the group consisting of halides (fluoride, chloride, bromide and
iodide), pseudohalides (cyanide, thiocyanide, cyanate),
carboxylates (formate, acetate, propionate, butyrate), alkyl
sulphite, alkyl sulphate, trifluoromethane sulfonate, phenyl
sulfonate, dialkyl phosphite, dialkyl phosphate, dialkyl
phosphonites, and dialkyl phosphonates, or ii) the ionic liquid is
replaced by NMMO.H.sub.2O or LiCl/DMAc.
7. The method according to claim 1, wherein the co-solvent is
selected from the group consisting of water, methanol, ethanol,
propanol, iso-propanol, butanol, acetone, acetonitrile,
dimethylsulfoxide, dimethylformamide, dimethylacetamide and
dimethylimidazolidione, preferably the co-solvent is water or
ethanol.
8. The method according to claim 1, wherein the co-solvent
comprises another ionic liquid which itself is not capable of
dissolving cellulose, so that this co-solvent-IL-mixture consists
of an aforementioned cation and any anion not mentioned above,
preferably of the type hexafluorophosphate, tetrafluoroborate,
bis(trifluoromethane)sulfonimide.
9. The method according to claim 1, wherein the ionic solvent has a
net basicity (.beta.-.alpha.) in the range 0.11-0.47; and a
.beta.-value in the range 0.57-0.95; preferably a net basicity
(.beta.-.alpha.) in the range 0.24-0.39; and a .beta.-value in the
range 0.70-0.88.
10. The method according to claim 1, wherein the ionic liquid is an
[emim]-based ionic liquid.
11. The method according to claim 1, wherein the ionic liquid is
[emim][OAc], [bmim][OAc], [emim][DMP], [DEP], [DBNH][OAc],
[DBNH][EtOAc], preferably [emim]OAc, or [emim][DMP], the co-solvent
is water or an alcohol, preferably water, wherein the water content
preferably is in the range 10-30 wt-%, and the solvent has a net
basicity (.beta.-.alpha.) in the range 0.11-0.47; and a
.beta.-value in the range 0.57-0.95; preferably a net basicity
(.beta.-.alpha.) in the range 0.24-0.39; and a .beta.-value in the
range 0.70-0.88.
12. The method according to claim 1, wherein the method is carried
out at a temperature ranging from 20-150.degree. C., preferably
40-80.degree. C. for a time ranging from 10-400 min, preferably
60-180 min.
13. The method according to claim 1, wherein the pulp consistency
is 1-25 wt-%, preferably 5-15 wt-%.
14. The method according to claim 1, wherein the hemicellulose-rich
pulp used as starting material is bleached or unbleached paper pulp
of any lignocellulosic raw material derived from any commercial
(sulphite, kraft, Soda-AQ) or non-commercial processes, such as
organosolv, carboxylic acid, ASAM, ASA or MEA.
15. The method according to claim 1, wherein the dissolved
hemicellulose fraction is regenerated by the addition of a
non-solvent, preferably water or alcohol, and the precipitate is
separated by filtration or centrifugation.
16. The method according to claim 1, wherein the dissolved
hemicellulose fraction is separated by pressure driven membrane
processes, and/or a non-solvent is added to the
hemicellulose-enriched retentate to initiate precipitation of the
hemicellulose, and the hemicellulose is recovered as a pure powder
after washing and drying.
17. The method according to claim 1, wherein the final cellulose
product obtained has a residual hemicellulose content of 1.0 to 10
wt-%, preferably between 2.0 and 5.0 wt-%, and the isolated and
purified hemicellulose has a residual cellulose content between 1.0
and 10 wt-%, preferably between 2.0 and 5 wt-%, wherein the
cellulose and hemicellulose contents are calculated by the Janson
formulae, and the neutral sugar contents are determined by
HPAEC-PAD as described in reference [10].
18. The method according to claim 1, wherein the cellulose-rich
residue is dissolved in a cellulose solvent.
19. The method according to claim 1, wherein oxidants or acids are
added to the cellulose dope to adjust the degree of polymerization
suitable for the subsequent forming and regeneration processes.
20. The method according to claim 1, wherein oxidants are added to
the cellulose dope to remove chromophores such as residual lignin,
HexA and extractives prior to the conversion processes.
21. The method according to claim 17, wherein the treated cellulose
dope is subjected to filtration to remove undissolved
impurities.
22. A dissolving cellulose pulp, obtained by a method according to
claim 1, wherein said cellulose pulp has a residual hemicellulose
content of 1.0 to 10 wt-%, preferably between 2.0 and 5.0 wt-%.
23. The dissolving cellulose pulp according to claim 22, obtained
by a method in which the isolated and purified hemicellulose,
withdrawn from a hemicellulose-rich source, has a residual
cellulose content between 1.0 and 10 wt-%, preferably between 2.0
and 5 wt-%, and wherein the cellulose and hemicellulose contents
are calculated by the Janson formulae, and the neutral sugar
contents are determined by HPAEC-PAD.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is entitled to the benefit of and
incorporates by reference subject matter disclosed in International
Patent Application No. PCT/FI2013/050414 filed on Apr. 15, 2013 and
U.S. Provisional Patent Application No. 61/646,383 filed May 14,
2012.
FIELD OF INVENTION
[0002] The invention relates to the separation of hemicellulose and
cellulose from polysaccharide sources. In particular, the present
invention relates to methods of separating hemicelluloses and
cellulose from hemicellulose-rich source, such as a pulp of any
origin or from holocellulose by dissolution in suitable solvents.
The present invention also relates to dissoloving pulps.
BACKGROUND
[0003] Dissolving pulp refers to pulp of high cellulose content
which is used as raw material for the manufacture of cellulose
derivatives and regenerated cellulose products. The wood-derived
dissolving pulps which account for about 85% of the total
dissolving pulp market are produced according to the acid sulphite
and prehydrolysis-kraft (PHK) processes. In both cases additional
purification steps such as hot and cold caustic extractions are
necessary to achieve the requested degree of purification
(determined as the content of residual hemicelluloses and alkali
resistance). The removal of the hemicelluloses is associated with
severe losses of cellulose mainly due to peeling-off reactions.
Cellulose losses comprise between 15 and more than 30 wt-%
depending on the process and the degree of purification. The
removed hemicelluloses are largely converted to low molar mass
hydroxy acids owing to alkaline post-extraction processes which
constitutes another drawback of the current technologies. Cotton
linters account for the residual 15% of the dissolving pulp market
and represent the dissolving pulp of highest cellulose purity. They
are particularly used for the production of acetate plastics and
high-DP cellulose ethers.
[0004] Contrary to the paper pulp market, the dissolving pulp
market shows a consistent annual growth of about 5% since the last
ten years after the man-made cellulose fiber industry was
consolidated during the 1990s. This growth is largely caused by the
installation of new viscose fiber capacities in Asia but more and
more also due to novel cellulose-based products requiring high
purity dissolving pulps. At the same time the availability of
cotton linters does not keep up with the increasing demand for
several reasons.
[0005] It has been estimated that the annual demand of dissolving
pulp will increase from currently 5-6 Mio t to about 12-20 Mio t in
2050, at least. This clearly underlines the need for novel
environmentally friendly and economically attractive manufacturing
processes for dissolving pulps of high purity which allow the
concomitant recovery of hemicelluloses in high yield and
purity.
SUMMARY
[0006] It is an aim of the present invention, to provide a means
for selectively and (almost) quantitatively dissolved
hemicelluloses from a hemicellulose-rich pulp of any origin as well
as from holocellulose in an ionic liquid of which the solvent
basicity and acidity are adequately adjusted by the addition of a
co-solvent.
[0007] The solvent basicity and acidity are characterized by the
Kamlet-Taft (KT) solubility parameters, primarily the b- (H-bond
basicity) and .alpha.- (H-bond acidity) values, respectively.
[0008] Thus, the present invention concerns a method for separation
of hemicellulose and cellulose by dissolution of hemicellulose from
a hemicellulose-rich pulp of any origin or from holocellulose.
[0009] In the present method hemicellulose is dissolved in a
solvent system comprising a cellulose solvent, which is either a
ionic liquid or another direct cellulose solvent, and a molecular
solvent (co-solvent), wherein said co-solvent does not dissolve
cellulose, and wherein the solvent basicity and acidity of said
ionic liquid or other direct cellulose solvent are adequately
adjusted by the co-solvent.
[0010] In an other aspect, this invention concerns a method for
separation of hemicellulose and cellulose by dissolution of
hemicellulose from a hemicellulose-rich pulp of any origin or from
holocellulose, wherein hemicellulose is dissolved in a solvent
system comprising a ionic liquid and a molecular solvent
(co-solvent), wherein said co-solvent does not dissolve cellulose
and wherein the solvent basicity and acidity of said ionic liquid
are adequately adjusted by the co-solvent.
[0011] In a third aspect, the present invention relates to
dissolving pulps.
[0012] More specifically, the present method is mainly
characterized by hemicellulose being dissolved in a solvent system
comprising a cellulose solvent, which is either a ionic liquid or
another direct cellulose solvent, and a molecular solvent
(co-solvent), wherein said co-solvent does not dissolve cellulose,
and wherein the solvent basicity and acidity of said ionic liquid
or other direct cellulose solvent are adequately adjusted by the
co-solvent and wherein hemicellulose is dissolved in a solvent
system comprising a ionic liquid and a molecular solvent
(co-solvent), wherein said co-solvent does not dissolve cellulose
and wherein the solvent basicity and acidity of said ionic liquid
are adequately adjusted by the co-solvent.
[0013] The dissolving pulps are characterized by cellulose pulp
having a residual hemicellulose content of 1.0 to 10 wt-%,
preferably between 2.0 and 5.0 wt-%.
Advantages
[0014] The present invention enables quantitative separation of
cellulose and hemicellulose without any depolymerization and yield
losses as occurring during conventional dissolving pulp
manufacturing processes. The invention facilitates the integration
of pulp refining into a cellulose regeneration process (IONCELL).
Hemicelluloses are dissolved by a solvent system with adjusted
solubility parameters instead of being fragmented by acid- or
alkaline catalyzed degradation routes (acid sulfite process
combined with hot caustic extraction or prehydrolysis kraft pulping
with our without post-alkaline extraction).
[0015] Some important advantages are:
[0016] (a) Simple process, low energy consumption: dissolution
treatment at slightly elevated temperature in a solvent system
which is equally suited for cellulose, cellulose+hemicellulose or
only hemicellulose dissolution. In this way this invention can be
expanded to cellulose regeneration processes.
[0017] (b) No yield losses of both hemicellulose and cellulose: at
the same level of cellulose purity, conventional
prehydrolysis-kraft process experiences 5 to 10% cellulose yield
loss on oven dry wood depending on the wood source and extent of
cellulose purity. The same applies to the acid sulfite pulping
process. Polymeric hemicelluloses cannot be recovered at all with
the existing dissolving pulp manufacturing processes. However, the
acid sulfite process allows to separate the dissolved monosugars
from the sulfite spent liquor (SSL).
[0018] (c) The invention suggests the use of a cellulose solvent
which can be also utilized in a conversion process, e.g. the
cellulose regeneration process. This allows the combination of the
pulp refining process (invention) with a fiber or film forming
process using the dry-wet regeneration concept as suggested for the
IONCELL process as mentioned above.
BRIEF DESCRIPTION OF DRAWINGS
[0019] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0020] FIG. 1: shows a simplified scheme of fractionating a
hemi-rich pulp into cellulose and hemicellulose fractions;
[0021] FIG. 2: shows cationic moieties of ionic liquids suitable of
pulp dissolution;
[0022] FIG. 3: shows net basicity, (.beta.-.alpha.), versus
basicity (.beta.) of [emim][OAc] mixed with increasing amount of
co-solvent. The co-solvent is water. The Kamlet-Taft (KT)
parameters have been determined at room temperature;
[0023] FIG. 4: shows glucan and xylan yields in the solid residue
as a function of the water content. The results are expressed a
wt-% on the amounts of glucan and xylan in the initial pulp;
[0024] FIG. 5: shows molar mass distribution of the initial
bleached birch kraft pulp, the pulp residue (dissolving pulp, i.e.
pure cellulose), the precipitate (extracted pure hemicellulose) and
the calculated sum of the fractions. The treatment was carried out
in [emim][OAc]-water with 15 wt-% water at 60.degree. C. for 3 h;
and
[0025] FIG. 6: shows molar mass distribution of the initial
bleached pine kraft pulp, the pulp residue (dissolving pulp, i.e.
cellulose), the precipitate (hemicellulose) and the calculated sum
of the fractions. The treatment was carried out with
[emim][OAc]-water with 15 wt-% water at 60.degree. C. for 3 h.
DETAILED DESCRIPTION
[0026] As discussed above, the present technology provides a novel
way of separating hemicellulose and cellulose by dissolution of
hemicellulose from a hemicellulose-rich source in a solvent system
comprising a cellulose solvent, which is either a ionic liquid or
another direct cellulose solvent, together with a molecular solvent
(co-solvent). The co-solvent is selected such that it does not
dissolve cellulose. The solvent basicity and acidity of said ionic
liquid or other direct cellulose solvent are adequately adjusted by
the co-solvent.
[0027] The solvent basicity and acidity are characterized by the
Kamlet-Taft solubility parameters, particularly by the .beta.-
(H-bond basicity) and .alpha.- (H-bond acidity) values.
[0028] To give some specific examples of preferred embodiment, in a
first embodiment, the ionic liquid is a direct cellulose solvent,
which has a cation selected from the group of cationic moieties
depicted in FIG. 2, wherein the residues R.sub.1-5 are
independently linear or branched alkyl- (typically C1-C6), alkoxy-,
or alkoxyalkyl groups, residues containing aryl moieties, or
hydrogen, and an anion selected from the group consisting of
halides (fluoride, chloride, bromide and iodide), pseudohalides
(cyanide, thiocyanide, cyanate), carboxylates (formate, acetate,
propionate, butyrate), alkyl sulphite, alkyl sulphate,
trifluoromethane sulfonate, phenyl sulfonate, dialkyl phosphite,
dialkyl phosphate, dialkyl phosphonites, and dialkyl
phosphonates.
[0029] In a preferred embodiment, the ionic solvent has a net
basicity (.beta.-.alpha.) in the range 0.11-0.47; and a
.beta.-value in the range 0.57-0.95; preferably a net basicity
(.beta.-.alpha.) in the range 0.24-0.39; and a .beta.-value in the
range 0.70-0.88.
[0030] In the present technology, the ionic liquid can also be
replaced by NMMO.H2O or LiCl/DMAc.
[0031] The co-solvent is preferably miscible with the ionic liquid.
In particular, the co-solvent is capable of lowering the
.beta.-value and/or raising the .alpha.-value of the solvent
system.
[0032] Preferably, the co-solvent is selected from the group
consisting of water, methanol, ethanol, propanol, iso-propanol,
butanol, acetone, acetonitrile, dimethylsulfoxide,
dimethylformamide, dimethylacetamide and dimethylimidazolidione,
preferably the co-solvent is water or ethanol.
[0033] In one particular embodiment, the co-solvent comprises
another ionic liquid which itself is not capable of dissolving
cellulose, so that this co-solvent-IL-mixture consists of an
aforementioned cation and any anion not mentioned above, preferably
of the type hexafluorophosphate, tetrafluoroborate,
bis(trifluoromethane)sulfonimide.
[0034] Preferably, the ionic liquid is an [emim]-based ionic
liquid.
[0035] Specific examples of ionic liquid are the following:
[emim][OAc], [bmim][OAc], [emim][DMP] and [DEP], [DBNH][OAc],
[DBNH][EtOAc], preferably [emim]OAc and [emim][DMP].
[0036] The co-solvent (to be combined with any of the above ionic
liquids is water or an alcohol, preferably water, wherein the water
content preferably is in the range 10-30 wt-%, and the solvent has
a net basicity (.beta.-.alpha.) in the range 0.11-0.47; and a
.beta.-value in the range 0.57-0.95; preferably a net basicity
(.beta.-.alpha.) in the range 0.24-0.39; and a .beta.-value in the
range 0.70-0.88.
[0037] The present method can be carried out, for example, at a
temperature ranging from 20-150.degree. C., preferably
40-80.degree. C. for a time ranging from 10-400 min, preferably
60-180 min.
[0038] Pulp consistency can vary within broad ranges, typically
being about 1-25 wt-%, preferably 5-15 wt-%.
[0039] The hemicellulose-rich pulp used as starting material can be
any bleached or unbleached paper pulp of any lignocellulosic raw
material derived from any commercial (sulphite, kraft, Soda-AQ) or
non-commercial processes, such as organosolv, carboxylic acid,
ASAM, ASA or MEA, although these examples are not exhaustive.
[0040] The dissolved hemicellulose fraction can be regenerated by
the addition of a non-solvent, preferably water or alcohol, and the
precipitate is separated by filtration or centrifugation.
[0041] In a further embodiment, the dissolved hemicellulose
fraction is separated by pressure driven membrane processes, and/or
a non-solvent is added to the hemicellulose-enriched retentate to
initiate precipitation of the hemicellulose, and the hemicellulose
is recovered as a pure powder after washing and drying.
[0042] Based on the above embodiments, a cellulose product can be
obtained which has a residual hemicellulose content of 1.0 to 10
wt-%, preferably between 2.0 and 5.0 wt-%, and the isolated and
purified hemicellulose has a residual cellulose content between 1.0
and 10 wt-%, preferably between 2.0 and 5 wt-%.
[0043] Typically, the cellulose and hemicellulose contents are
calculated by the Janson formulae, and the neutral sugar contents
are determined by HPAEC-PAD as described in reference [10].
[0044] The cellulose-rich residue can, for example, be dissolved in
a cellulose solvent as mentioned above.
[0045] Modifications of the above methods are possible. Thus, for
example oxidants or acids can be added to the cellulose dope to
adjust the degree of polymerization suitable for the subsequent
forming and regeneration processes. The amount of such oxidants or
acids is typically 0.001 to 10% by weight of the total
composition.
[0046] The oxidants added to the cellulose dope can be selected so
as to be capable of removing chromophores such as residual lignin,
HexA and extractives prior to the conversion processes.
[0047] The treated cellulose dope is subjected to filtration to
remove undissolved impurities.
[0048] Turning now to the drawings, it can be noted that FIG. 1
shows a simplified scheme of the fractionation process. Thus, in
the scheme, pulp was treated with a solvent system in a vertical
kneader (or a stirrer at smaller scale) at various temperatures
(60-80.degree. C.) and retention times (0.5-6 h). The solvent
system consisted of an [emim][OAc]-water mixture with a water
content ranging between 10 wt-% and 30 wt-%. The resulting
suspension was filtered (separated) with a press filter (or a
centrifuge). The dissolved xylan was precipitated by further
addition of water (non-solvent). The washed and dried cellulose and
xylan fractions were analysed.
[0049] The solvent systems typically comprise an ionic liquid and a
molecular solvent of which the latter is usually used in minor
parts and, thus, can be stripped off easily to regenerate the ionic
liquid. The herein presented concept is valid for all ionic liquids
that were reported as cellulose solvents. This comprises in
particular ionic liquids with cationic moieties such as depicted in
FIG. 2. The residues R.sub.1-5 are independently linear or branched
alkyl- (typically C.sub.1-C.sub.6), alkoxy-, or alkoxyalkyl groups,
residues containing aryl moieties, or hydrogen.
[0050] The preferred anions of the ionic liquids are halides
(fluoride, chloride, bromide and iodide), pseudohalides (cyanide,
thiocyanide, cyanate), carboxylates (formate, acetate, propionate,
butyrate), alkyl sulphite, alkyl sulphate, trifluoromethane
sulfonate, phenyl sulfonate, dialkyl phosphite, dialkyl phosphate,
dialkyl phosphonites, dialkyl phosphonates (FIG. 2). Thus, the
resulting ionic liquid is hydrophilic and its Kamlet-Taft basicity
and net-basicity suitable for cellulose dissolution [7].
[0051] To generate a solvent system that allows aforementioned
fractionation of holocellulose, the ionic liquid is mixed with a
co-solvent. Any solvent that does not dissolve cellulose itself can
be utilized as co-solvent to generate a selective solvent system.
Preferred co-solvents are miscible with the respective ionic liquid
and lower the b value (and/or raising the a value, respectively) of
the resultant solvent mixture. Preferably, the co-solvent is water,
methanol, ethanol, propanol, iso-propanol, butanol, acetone,
acetonitrile, dimethylsulfoxide, dimethylformamide,
dimethylacetamide, dimethylimidazolidione. The co-solvent can also
comprise another ionic liquid which itself is not capable of
dissolving cellulose. This co-solvent-IL consists of an
aforementioned cation and and any anion not mentioned above,
preferably of the type hexafluorophosphate, tetrafluoroborate,
bis(trifluoromethane)sulfonimide. For environmental and energy
saving reasons, water and ethanol are used more preferably.
[0052] In addition to ionic liquids also other direct cellulose
solvents, preferably NMMO.H.sub.2O and LiCl/DMAc, are suitable for
the selective dissolution of low molar mass polysaccharides such as
hemicelluloses or low molar mass cellulose from a
hemicellulose-rich pulp when mixed with a co-solvent--as listed
above--in a ratio so that the targeted solvent parameters (net
basicity, b value) are adequately adjusted.
[0053] The Kamlet-Taft (KT) parameters have been proven to be
useful solvent property indicators [1]. They are determined from
the absorption peaks of the three dyes Reichardt's dye (RD, range
518-585 nm), N,N-diethyl-4-nitro-aniline (DENA, 402-414 nm) and
4-nitroaniline (NA, 406-398 nm). The peaks are typically fitted to
a Gaussian function in order to precisely locate the maxima
(v.sub.max). From these functions v.sub.max(T), the E.sub.T(30),
.pi.*, .alpha. and .beta. parameters are calculated using published
equations [2].
[0054] Several authors have demonstrated that the H-bond basicity,
expressed by the b-value, correlates with the capability of an
ionic liquid to dissolve cellulose [2-6]. Other KT values were not
found to correlate directly with the dissolution of cellulose.
[0055] Quite recently, we introduced the net basicity term,
.beta.-.alpha., which allows a better prediction of both
dissolution and regeneration of cellulose since it accounts for the
acidity imparted by the cation or a protic co-solvent [7]. Based on
a representative selection of cellulose solvents it was shown that
cellulose dissolution generally conform to the requirement
0.35<.beta.-.alpha.<0.9 with b>0.8 [7]. With the
progressive addition of a protic co-solvent such as water or
alcohol the H-bond basicity, b, decreases while the H-bond acidity,
a, increases. This was demonstrated by adding water to [emim][OAc].
As shown in FIG. 3, the net basicity decreases faster than the
b-value due to the opposite development of the b- and a-values with
increasing amount of water in [emim][OAc]. Further, FIG. 3 reveals
the ranges of the KT derived solubility parameters indicating
complete and partial dissolution of hemicelluloses from paper-grade
pulps.
[0056] As expected, the solubility of a hemicellulose-rich pulp
decreases with an increasing percentage of water in an
[emim][OAc]-water mixture when treated for three hours at about
60.degree. C. in a vertical kneader.
[0057] Surprisingly, the extent of pulp dissolution decreases only
gradually with increasing water concentration in [emim][OAc]. This
was not expected since for some ionic liquids, e.g. for [bmim]Cl,
the TMG-based ILs and others, it was known that the presence of
only marginal amounts of water resulted in a complete stop of their
capability to dissolve even fractions of a pulp [7][9]. The
[emim][OAc]-water mixture, however, revealed high dissolution power
even at relatively high water concentration. This was for example
demonstrated for a bleached kraft pulp of which 60 wt-%, 28 wt-%,
20 wt-%, 13 wt-% and 1 wt-% were dissolved in [emim][OAc]-water
mixtures with a water content of 10 wt-%, 15 wt-%, 20 wt-%, 25 wt-%
and 30 wt-%, respectively. Beyond 30 wt-% water in
[emim][OAc]-water dissolution of any pulp component stops.
[0058] A closer examination confirmed that the extent of
dissolution and thus the dissolution power of the solvent system
were mainly related to the molar mass of the pulp components.
Factors such as the pulp morphology, supramolecular structure,
degree of crystallinity and chemical properties (e.g. affecting
hydrophilicity) of the pulp components are likely to affect the
solution behaviour as well. The removal of pure hemicellulose and
hemicellulose fractions from paper pulp was, however, unforeseeable
despite the expected molar mass dependent pulp fractionation
behavior of the [emim][OAc]-water solvent. The solvent properties
of appropriate [emim][OAc]-water mixtures were obviously more
favourable for the extraction of hemicellulose than for cellulose
of comparable molar mass.
[0059] The results shown in FIG. 4 clearly indicate that xylan from
a birch kraft pulp is most efficiently and selectively dissolved in
[emim][OAc] containing 15-20 wt-% of water. Beside the water
content of the solvent system, the efficiency and selectivity of
hemicellulose dissolution were also affected by the dissolution
conditions. This was demonstrated for a solvent mixture containing
20 wt-% of water. The results of different dissolution conditions
for this particular water content of the solvent mixture are
included in FIG. 4. The detailed results are presented in Example
3.
[0060] Based on the above, dissolving cellulose pulps are provided,
wherein the cellulose pulps have a residual hemicellulose content
of 1.0 to 10 wt-%.
[0061] Thus, a dissolving cellulose pulp obtained by a method as
explained in the foregoing, in which the isolated and purified
hemicelluloses is withdrawn from a hemicellulose-rich source,
exhibits a residual cellulose content between 1.0 and 10 wt-%,
preferably between 2.0 and 5 wt-%, the cellulose and hemicellulose
contents being calculated by the Janson formulae, and the neutral
sugar contents are determined by HPAEC-PAD as described in
reference [10].
[0062] The following non-limiting Examples illustrate the
invention,
EXAMPLE 1
[0063] Effect of the Water Content in [emim][OAc] on the
Fractionation of a Commercial Birch Kraft Pulp: Composition of the
Pulp Residue
[0064] ECF-bleached birch kraft pulp was treated with an
[emim][OAc]-water mixture [10 wt-% to 30 wt-%] in a horizontal
kneader for 3 h at 60.degree. C. The subsequent phase separation
was conducted with a filter press equipped with a metal fleece. The
pore diameter was in the range 1-5 .mu.m. The pulp residue was
thoroughly washed with water, dried and subjected to analysis.
Alternatively, the dissolution was supported by a stirrer and the
phase separation by centrifugation. The results are summarized in
Table 1.
TABLE-US-00001 TABLE 1 Effect of the water content in [emim][OAc]
on the efficiency and selectivity of xylan removal.
Characterization of the pulp residue. H.sub.2O, Temp Xylan
Viscosity Trial wt-% Consistency, % Conditions .degree. C. Time h
Yield % content % mL/g Initial 100.0 23.1 808 Birch Pulp trial 3 10
3.3 kneader, 60 3 40.0 4.0 1040 filtration trial 1 15 3.3 kneader,
60 3 64.7 2.5 981 filtration trial 167 17.5 3.3 kneader, 60 3 76.1
3.9 954 filtration trial 164 20 3.3 kneader, 60 3 76.2 6.8 921
filtration trial 5 22.5 3.3 kneader, 60 3 90.0 9.6 886 filtration
trial 2 25 3.3 kneader, 60 3 86.1 14.6 891 filtration trial 4 30
3.3 kneader, 60 3 98.8 21.4 808 filtration
EXAMPLE 2
[0065] Effect of the Water Content in [emim][OAc] on the
Fractionation of a Commercial Birch Kraft Pulp: Composition of the
Precipitated Soluble Fraction
[0066] The soluble fractions generated in Example 1 were
precipitated by the addition of excess water (anti-solvent). The
precipitated, extracted polysaccharides were centrifuged and washed
thoroughly to remove the residual ionic liquid. The washed
precipitates were dried at room temperature over night or,
alternatively, by freeze drying. Table 2 shows the yield and the
composition of the extracted low-molar mass pulp fractions.
TABLE-US-00002 TABLE 2 Effect of the water content in [emim][OAc]
on the yield and purity of the extracted pulp fraction.
Characterization of the precipitate from the soluble fraction. Mw
(GPC) H.sub.2O, Temp Cellulose* Pullulan Trial wt-% Consistency, %
Conditions .degree. C. Time h Yield % content, % [kDa] Initial 0
Birch Pulp trial 3 10 3.3 kneader, 60 3 60.0 50.5 609.1 filtration
trial 1 15 3.3 kneader, 60 3 35.3 3.7 23.4 filtration trial 167
17.5 3.3 kneader, 60 3 23.9 2.8 n.a. filtration trial 164 20 3.3
kneader, 60 3 23.8 n.a. n.a. filtration trial 5 22.5 3.3 kneader,
60 3 10.0 1.8 19.7 filtration trial 2 25 3.3 kneader, 60 3 13.9 2.0
21.9 filtration trial 4 30 3.3 kneader, 60 3 1.2 9.1 26.0
filtration *calculated according to the Janson formulae [8]
[0067] Table 2 shows that between a water content of 10 to 15 wt-%
in [emim][OAc] the transition from cellulose/hemicellulose to pure
hemicellulose extraction occurs. Thus, in the range between 15 wt-%
and 25 wt-% of water basically only hemicellulose is extracted.
Quantitative hemicellulose extraction is achieved in the range
between 15 wt-% and 20 wt-% of water content in [emim][OAc] at
least.
EXAMPLE 3
[0068] Effect of Dissolution Conditions at a Constant Water Content
of 20 wt-% in [emim][OAc] on the Fractionation Efficiency and
Selectivity of a Commercial Birch Kraft Pulp
[0069] In a series of experiments, where the water content was kept
constant at 20 wt-% in [emim][OAc], the effects of temperature,
time and mixing conditions on the fractionation of a bleached birch
kraft pulp have been determined (table 3).
TABLE-US-00003 TABLE 3 Effect of temperature, time and mixing
conditions at a water content of 20 wt- % in [emim][OAc] on the
yield and purity of the pulp residue H.sub.2O, Temp Xylan Viscosity
Trial wt-% Consistency, % Conditions .degree. C. Time h Yield %
content % mL/g Initial 0 Birch Pulp trial 164 20 3.3 kneader, 60 3
76.2 6.8 921 filtration trial 155 20 3.3 stirrer, 60 3 81.3 6.2 906
centrifuge trial 157 20 3.3 stirrer, 60 6 75.6 1.9 n.a. centrifuge
trial 159 20 3.3 stirrer, 80 3 82.1 1.8 914 filtration trial 160 20
3.3 stirrer, 60 0.5 78.7 8.5 907 centrifuge trial 161 20 3.3
ultrasonication 60 3 80.2 1.5 920 trial 162 20 3.3 ultrasonication
60 6 79.6 1.8 n.a.
[0070] The support through longer retention time, higher
temperature and the concomitant application of ultrasonication
revealed a clear impact on the yield and purity of the pulp
residue.
[0071] High temperature (80.degree. C., 3 h) or moderate
temperature combined with long dissolution time (60.degree. C., 6
h) show significant better xylan dissolution efficiency as compared
to standard conditions (60.degree. C., 3 h). Further, the support
of dissolution by ultrasonication seems to improve the
efficiency/selectivity of xylan removal significantly. The xylan
content of the pulp residue decreases to only 1.5 to 1.8% od, which
fulfill the requirements for standard acetate grade pulps.
EXAMPLE 4
[0072] Effect of Pulp Consistency in the Solvent System
[emim][OAc]-Water on the Fractionation Efficiency and Selectivity
of a Commercial Birch Kraft Pulp.
[0073] Pulp consistency in a suspension or solution has an
important impact on the economic feasibility of a process. Most
experiments were conducted at a rather low consistency of 3.3 wt-%
to facilitate the handling of the pulp-solvent system in the lab.
The pulp consistency was increased to 10.5 wt-% in a separate
experiment with bleached birch kraft pulp using [emim][OAc] with a
water content of 15 wt-%. The results are compared with those
achieved at a pulp consistency of only 3.3 wt-% in Table 4.
TABLE-US-00004 TABLE 4 Effect of pulp consistency at a water
content of 15 wt-% in [emim][OAc] on the yield and purity of the
pulp residue H.sub.2O, Temp Xylan Viscosity Trial wt-% Consistency,
% Conditions .degree. C. Time h Yield % content % mL/g Initial 0
Birch Pulp trial 1 15 3.3 kneader, 60 3 64.7 2.5 981 filtration
trial 6 15 10.5 kneader, 60 3 73.1 2.7 969 filtration
[0074] Besides the yield of the residue, which was very difficult
to determine, the performance at 10.5 wt-% consistency was
comparable to that at 3.3 wt-% consistency (the yield of the former
is more reliable considering mass balance). Evidence of the
quantitative and highly selective fractionation of cellulose and
hemicellulose from a hemicellulose-rich pulp has been provided by
the comparative evaluation of the molar mass distributions of the
initial pulp, the cellulose and hemicellulose fractions and their
calculated sums. In this way it was shown that fractionation occurs
in a highly selective and quantitative way. Thus, no degradation of
cellulose or hemicellulose was observed as occurring during the
conventional dissolving pulp processes.
EXAMPLE 5
[0075] Effect of Wood Raw Material: Birch vs. Pine Kraft Pulp
[0076] The fractionation performance of the solvent system
[emim][OAc]-water with a water content of 15 wt-% was investigated
for a pine kraft pulp in comparison to a birch kraft pulp. The
results are summarized in Table 5.
TABLE-US-00005 TABLE 5 Effect of wood raw material of a paper grade
kraft pulp on the yield and purity of the pulp residue. Treatment
conditions: 85 wt-% [emim][OAc] + 15 wt-% water, 60.degree. C., 3 h
in a kneader, phase separation with a press filter H.sub.2O, Temp
Cellulose, Xylan GGM Viscosity Trial wt-% Consistency, % .degree.
C. Time, h Yield % %* %* %* mL/g Initial birch 100.0 70.3 28.7 1.0
808 pulp treated 15 3.3 60 3 64.7 96.7 3.3 0.0 981 birch pulp,
trial 1 Initial pine 100.0 82.3 9.7 8.0 832 pulp treated 15 3.3 60
3 77.5 96.2 1.5 2.3 932 pine pulp, trial 7 *calculated according to
the Janson formulae [8]
[0077] The successful separation of cellulose and hemicelluloses
from a pine kraft pulp is also reflected in their molar mass
distributions (FIG. 6). From the results it can be concluded that
softwood and hardwood kraft pulps are equally suited as substrate
for the quantitative separation of hemicellulose and cellulose by
applying the process according to the present invention.
[0078] Examples 1-5 confirm the viability of the novel
fractionation concept of hemicellulose-rich pulps (holocellulose,
paper-grade pulps) using an IL-co-solvent mixture with suitable
solvent parameters as expressed by the KT-parameters and
appropriate dissolution conditions (FIG. 3).
[0079] With reference to work on the dissolution of cellulose [7]
conditions can now be proposed allowing the complete and partial
dissolution of hemicelluloses from hemicellulose-rich
polysaccharides, preferred from bleached paper grade pulps.
[0080] FIG. 3 shows the solubility window for the complete
(.beta.-.alpha.=0.24-0.39; .beta.=0.70-0.88) and the complete and
partial (.beta.-.alpha.=0.11-0.47; .beta.=0.57-0.95) dissolution of
hemicelluloses.
[0081] The appropriate solvent properties have been conveniently
adjusted by the addition of water to [emim][OAc]. However, the
fractionation concept can be successfully transferred to any
cellulose solvent-co-solvent mixture provided that the solubility
parameters fulfil the requirements as defined for the hemicellulose
dissolution window (complete and partial).
[0082] Different to conventional and novel fractionation schemes
for the manufacture of dissolving pulp using chemical reactions,
the proposed invention allows a quantitative separation of
hemicelluloses and cellulose of high purity without any losses and
the depolymerisation of the associated polymers.
[0083] Supporting the extraction by high intensity mixing at
elevated temperature promotes the fractionation efficiency and
selectivity as exemplified in Table 3.
[0084] Quantitative separation of cellulose and hemicellulose of
hemicellulose-rich pulps or holocellulose, is embedded in a new
process concept, IONCELL, which, as a first step, comprises the
separation of the hemicellulose from the original
hemicellulose-rich substrate. Step 2 of the IONCELL process is
characterized by the separation of the dissolved hemicellulose
after phase separation. The separation is preferentially conducted
by membrane separation to avoid any further dilution of the solvent
(e.g. ionic liquid).
[0085] Alternatively, the addition of a non-solvent, preferably
equivalent to the co-solvent (e.g. water), is added to the solution
to precipitate the hemicellulose (FIG. 1). An appropriate
filtration of the generated hemicellulose/solvent/co-solvent
suspension ensures a quantitative phase separation. The filtrated
hemicellulose is washed and dried while the solvent/non-solvent
mixture is recycled to the fractionation process after the
co-solvent content has been adjusted to the desired value.
[0086] In a third step, the purified cellulose fraction is
dissolved in a cellulose solvent, e.g. ionic liquid, recycled
either from the conversion (fibre, film) or from the fractionation
process. The dope may be further treated by oxidants (bleaching
chemicals like hydrogen peroxide, ozone and others) to remove
impurities (bleaching) in the case of an unbleached pulp as initial
substrate and/or to adjust the degree of polymerization as
requested by subsequent forming and regeneration processes. Those
processes comprise primarily the production of regenerated fibers
and films.
[0087] While the present invention has been illustrated and
described with respect to a particular embodiment thereof, it
should be appreciated by those of ordinary skill in the art that
various modifications to this invention may be made without
departing from the spirit and scope of the present.
* * * * *