Induction of lignin solubility for a series of polar ionic liquids by the addition of a small amount of water

Article abstract of DOI:10.1039/c7gc00626h

Addition of a small amount of water was found to induce the lignin solubilizing ability in several polar ionic liquids which showed no lignin solubility in the absence of water. Similarly, addition of water was found to enhance lignin solubility in many polar ionic liquids. Though addition of water lowered the proton accepting ability of these ionic liquids, their proton donating ability was found to increase. The lignin dissolution by ionic liquids was newly found to be a function of both the proton accepting ability and proton donating ability of the ionic liquids. Water is a poor solvent for polysaccharides, and water addition has therefore been confirmed to be effective to improve the selective extraction yield of lignin from cedar powder under mild conditions.

Full text of DOI:10.1039/c7gc00626h

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: T. Akiba, A.
Tsurumaki and H. Ohno, Green Chem., 2017, DOI: 10.1039/C7GC00626H.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Volume 18 Number
7 7 April 2016 Pages 1821–2242
Green
Chemistry
Accepted Manuscripts are published online shortly after
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Green Chemistry
Page 1 of 7
View Article Online
DOI: 10.1039/C7GC00626H
Journal Name
COMMUNICATION
Induction of lignin solubility for a series of polar ionic liquids by
the addition of small amount of water
Received 00th January 20xx,
Accepted 00th January 20xx
Takashi Akiba,a,b Akiko Tsurumaki,a,b and Hiroyuki Ohnoa,b
*
DOI: 10.1039/x0xx00000x
www.rsc.org/greenchem
Addition of small amount of water was found to induce obtained as high quality pulp and lignin is obtained as a black
lignin solubilizing ability of several polar ionic liquids which liquor residue.11 Though pulp is widely used to produce paper,
showed no lignin solubility in the absence of water. Similarly, the lignin recovered from black liquor is normally combusted
addition of water was found to enhance lignin solubility in to produce energy.
Because black liquor contains
many polar ionic liquids. However addition of water lowered depolymerised polysaccharides due to harsh treatment, lignin
proton accepting ability of these ionic liquids, their proton obtained as a precipitation after neutralization of black liquor
donating ability was found to increase. The lignin dissolution is also contaminated by saccharide residues.12 These impurities
by ionic liquids was newly found to be the function of both in lignin are unfavourable to obtain pure lignin for further
proton accepting ability and proton donating ability of the application. Since it is economically difficult to produce value-
ionic liquids. Since water is a poor solvent for polysaccharides, added chemicals from lignin, lignin has been deemed as just a
water addition has been confirmed to be effective to improve by-product and incinerated as a fuel for kraft pulping process.
selective extraction yield of lignin from cedar powder under Thus, development of new methodology, which is able to
mild condition.
separate lignin under milder condition expecting not to extract
cellulose, is imperative for the effective use of lignin.
According to the method for lignocellulose treatment,
Introduction
Lignocellulose, consisting mainly of cellulose, hemicellulose, lignins are classified into alkaline lignin (AL), Klason lignin, kraft
and lignin, has attracted much attention as abundant and lignin, organosolv lignin, lignosulfonate, and so on. Among
renewable feedstock.1 As polysaccharides such as cellulose these technical lignins, AL was chosen as a target in this work
and hemicellulose have been utilized in pulp industry and because of its moderately low molecular weight and simple
13
currently used as a raw material for chemicals, lignin has also structure. In contrast to this, Klason lignin has large number
attracted attention as a renewable aromatic chemical stock.2 of three-dimensional crosslinks and kraft lignin has thioether
However, utilization of lignin is still under development bond, respectively, which are different from lignin in
because insolubility of lignin in organic solvent limits the nature.14,15 In the case of organosolv lignin and lignosulfonate,
extraction of lignin from lignocellulose. Since the component these are soluble in organic solvents and water,
of lignocellulose entangles with each other as well as respectively.16,17 Accordingly, AL is considered to be a good
crosslinking, many attempts have been made to extract each model for the screening of novel solvents for lignin.
component by breaking these tough complexed structure.3-10
Recently, ionic liquids (ILs) have attracted attention as
The major method to extract each component is known as solvents for biomass processing.18 ILs having high hydrogen
“kraft pulping process” in which biomass was added and donating ability can dissolve cellulose. In the initial stage,
treated in sodium hydroxide/sodium sulphide mixture to break [C4mim]Cl was found to dissolve cellulose at 100 °C.19 We
the crosslinking of lignin. Throughout this method, cellulose is have previously shown that Kamlet-Taft parameters of ILs (
hydrogen accepting ability and : hydrogen donating ability)
are quite useful to discuss dissolution ability of cellulose in
α :
β
21
ILs.20,
Not only cellulose but also lignin is targeted to
solubilise with ILs. It has been reported that some acidic
ILs22,23, imidazolium-type ILs24,25, cholinium-type ILs26,27 and
amino acid ILs28 are known as good solvents for fragmented
lignin. Several ordinary ILs such as diazabicycro-type29 and
onium-type ILs30 are also known as their solvents.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 7
View Article Online
DOI: 10.1039/C7GC00626H
COMMUNICATION
Journal Name
Furthermore, these solubility data cannot be compared In case of samples treated under harsh condition, some
because of different properties of these lignin samples. aromatic rings may be damaged and deviated from the
Accordingly, there is
a strong request on the general relation between concentration of dissolved lignin and
understanding to obtain ILs with high lignin dissolution ability. absorbance. We have checked this relation is effective for
o
It has been recently shown that addition of water to ILs lignin dissolved in some ILs treated at 60 C (see Fig. S2). For
enhances lignin dissolution31 but the reason of positive effect more direct measurement, we have checked the dissolution of
of water addition on the improvement of lignin solubility lignin by naked eyes and optical microscopic observation.
remains unknown. Hart et al. have previously reported Extraction of lignin from cedar powder
solubility of organosolv lignin in a series of ILs.24 They have To ILs or their mixtures with water, 5.0 wt% of Cedar powder
chosen ILs having different polarity to conduct systematic was added and stirred at 60 °C for 10 hrs. The mixture was
investigation. They have found that cation structure affected centrifuged at 15,000 rpm for 10 min. to separate insoluble
lignin dissolution greater than that of anion. We have focused residue. Concentration of dissolved lignin (Clignin in wt%) in the
on Kamlet-Taft parameters for quantitative study of lignin liquid phase was evaluated using UV-Vis spectroscopy,
dissolution in ILs, especially on the effect of water addition.
because of the absorption by phenolic groups of AL at 280 nm
that was previously proposed by Hart et al24. The baseline was
recorded using ILs or IL/water mixture stirred at 60 °C for 10 h.
In order to obtain Clignin, a standard line was determined by
Experimental
Materials
Alkaline lignin (AL) and cedar powder prepared from Japanese plotting the absorbance of [C2mim]CH3O(H)PO2 dissolving
cedar were provided by Forestry and Forest Products Research defined amount of AL and added weight of AL. Clignin was
Institute (FFPRI), Japan. AL was washed with water and calculated by substituting measured absorbance for the linear
filtrated three times to remove acid residue which was equation (see Fig. S2). Weight of the extracted lignin (Wlignin
)
contaminated during extraction of AL. Absence of acid was was then calculated from Eq.1, where WCP is weight of the
confirmed by checking pH of the aqueous dispersion of AL. added cedar powder and Wsolvent is weight of used solvent.
Wlignin = (W CP + W solvent) × Clignin / 100 ･･･Eq.1
The AL and cedar powder were dried in vacuo at room
temperature and sieved (75-150 μm). A series of [C2mim] salts
containing such anions as CH3SO3, dicyanamide (N(CN)2),
bis(trifluoromethanesulfonyl)imide ([Tf2N]), and BF4 were
purchased from Tokyo Chemical Industry Co., Ltd.
[C2mim]CH3O(H)PO2 was purchased from Kanto Chemical Co.,
The Wlignin out of the quantity of lignin contained in the added
cedar powder was defined as the extracted degree of lignin
(%Elignin) as shown in Eq.2. The weight of lignin in the cedar
powder was estimated to be 32.6% of WCP according to Klason
method.32
Inc.
1-Hydroxyethyl-3-methyimidazolium
[Tf2N]
%Elignin = Wlignin / (WCP
× 0.326) ･･･Eq.2
([C2OHmim][Tf2N]),
tetrabutylphosphonium
dicyanamide
([P4444]N(CN)2), [P4444]CH3O(H)PO2, and a series of [C2mim] salts
containing such anions as CH3CO2, CF3CO2, CF3SO3, as well as a
series of CF3CO2 salts containing tetrabutylphosphonium
([P4444]), N-butyl-N-methyl-piperidinium([Pip14]), N-butyl-N-
Results and discussion
Effect of water content on the solubility of AL in ILs
Solubility of AL in a series of [C2mim] salts and their mixtures
with water was evaluated. One of polar IL, [C2mim]CF3SO3,
could dissolve no AL at 60 °C, but it was newly found that this
dissolved 40 wt% of AL at 60 °C when 10-20 wt% of water was
added. It was also confirmed that [C2mim]CF3SO3 dissolved
lignin even at room temperature in the presence of water.
Though there is a fact that addition of water dropped solubility
of polysaccharides in ILs33, addition of water induced
dissolution of AL. Furthermore, addition of only 1.0 wt% water
was confirmed to induce solubility of AL in [C2mim]CF3SO3.
Improvement of AL solubility was also observed as shown in
Fig. 1(b) and Fig. S3 when [C2mim]CH3CO2, [C2mim]CH3O(H)PO2,
and [C2mim]CF3CO2 were used. In the case of [C2mim]CH3CO2,
up to 50 wt% of AL was dissolved in the presence of water. In
contrast to this, induction and improvement of AL solubility
was not observed for [C2mim]BF4 and [C2mim][Tf2N]. From
these results, water addition was shown to be effective to
dissolve AL only when certain ILs were used. Anion structure
was also confirmed to strongly affect the solubility of AL even
in the presence of water. The effect of cation structure on the
solubility of AL was then analysed using a series of CF3CO2 salts.
The CF3CO2 salts were selected by considering its high stability
in the presence of water and low melting point compared to
methylpyrrolidinium([Pyr14]),
and
N-butyl-N-
methylmorpholinium ([Mor14]) were prepared as shown in the
ESI.
Dissolution test of alkaline lignin
All ILs were dried in vacuo at 80 °C for 10 h. Water content of
these ILs was confirmed to be less than 0.2 wt% by Karl Fischer
titration. Then, Milli-Q® water was added to the ILs. To
pristine ILs or IL/water mixtures, 10 wt% of AL was added and
stirred at 60 °C for 30 min. Solubility was checked with optical
microscope observation as well as by naked eyes. When
added AL was dissolved completely, another 10 wt% of AL was
added, and their solubility was evaluated in the same manner.
To determine the maximum dissolution amount of AL, this
procedure was repeated until undissolved AL was observed.
For ILs having solubilisation ability of AL at 60 °C, the
dissolution test was also carried out at room temperature. For
this test under mild condition, 1.0 wt% of AL was added to IL
and stirred for half a day. To confirm reproducibility of the
obtained results, all the dissolution tests were conducted twice.
Concentration of lignin in the liquid phase can be evaluated
using UV-Vis spectroscopy. The absorption by phenolic groups
of lignin at 280 nm is useful as Hart et al previously proposed24.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 3 of 7
View Article Online
DOI: 10.1039/C7GC00626H
Journal Name
COMMUNICATION
Table 1 β value and solubility of 10 wt% AL in a series of (a)
[C2mim] salts and (b) CF3CO2 salts.
(a) [C2mim]CF3SO3
(b) [C2mim]CH3CO2
60
40
60
40
(a) [C2mim] salts
(b) [CF3CO2] salts
Solubility of AL
Solubility of AL
β
value
β value
Anion
#
Cation
#
10wt%
aq.
10wt%
(neat)
(neat)
20
20
neat
neat
aq.
+
+
0
0
1
CH3CO2¯
1.06
○
○
○
○
○
×
×
×
○
○
○
○
○
○
×
×
9
[P4444
]
1.06
0.86
0.85
×
×
○
○
×
○
○
○
○
○
Concentraion 20of water30 wt%
0
40
0
10
40
Conc10entration20of water30 wt%
2 CH3O(H)PO2¯ 1.00
10 [Pip14
]
Fig. 1 Effect of water concentration on the solubility of AL in
(a) [C2mim]CF3SO3 and (b) [C2mim]CH3CO2 at 60 oC.
+
3
4
5
6
7
8
CF3CO2¯
CH3SO3¯
N(CN)2¯
CF3SO3¯
BF4¯
0.75
0.72
0.61
0.47
0.37
0.22
11 [Pyr14]
[C2mim]+ 0.84
(a) [P4444]CF3CO2
(b) [Pyr14]CF3CO2
3
60
40
60
+
]
12 [Mor14
0.71
40
20
0
20
0
Con10centraion20of water wt%
0
30
40
0
30
40
Con10centraion20of water wt%
[Tf2N]¯
Fig. 2 Effect of water concentration on the solubility of AL in
(a) [P4444]CF3CO2, (b) [Pyr14]CF3CO2 at 60 oC.
ability in the absence of water. In addition to the irrelevance
between value and AL solubility, water addition is known to
lower value of ILs which is certainly unfavourable for AL
dissolution. This strongly suggests the existence of other
factors to affect solubility of AL in ILs. In spite that the value
has been empirically known to less affect the dissolution of
β
other salts we have investigated in this study. [Pyr14]CF3CO2
dissolved AL after water addition (<40 wt%). Other ILs such as
[Mor14]CF3CO2, [P4444]CF3CO2, and [Pip14]CF3CO2 enhanced
solubility of AL only after adding water (Figs. 2 and S4). All
CF3CO2 salts investigated here dissolved AL even at room
temperature when water was added.
β
α
these polymers containing lots of hydroxyl groups than
we have reached one point to check the effect of both
values for the dissolution of lignin.
β
α
value,
and
β
Effect of water addition on the solubility of AL from the
viewpoint of Kamlet-Taft parameters
Factors affecting the solubility of AL in ILs containing water
Effect of Kamlet-Taft parameters of ILs on the solubility of AL
was addressed. Kamlet-Taft parameters are often used to
We then focused on the solubility of AL in the ILs containing
water. Decrease of AL solubility at high water content is
considered to be due to the dilution of ILs as well as poor
solubilising properties of water. In contrast to this,
improvement of AL solubility at low concentration of water is
considered to be attributed to change in viscosity and/or
solvent-solute interaction. However the effect of viscosity
greatly affects the dissolution speed of AL, addition of water
less affects on the dissolution amount. Considering this, the
improvement of AL solubility may be triggered by the change
of solvent-solute interaction.
describe polarity of solvents, especially α and β values are
known to denote the hydrogen donating ability and accepting
ability, respectively. We have previously shown that ILs with
high hydrogen accepting ability, i.e., high
β value, are
favourable for dissolution of cellulosic biomass.20, 21 Because,
in the case of cellulose dissolution, inter- and intra-molecular
hydrogen bonds in cellulose crystals are broken by ILs having
high
β
value. In addition to this, there are several reports
value dissolve kraft
suggesting that ILs with mid to high
β
lignin.18 Considering that lignin also contains many OH groups,
there are some contributions of hydrogen bonds between
these OH groups. It is also considered to be necessary to break
these hydrogen bonds for the dissolution of oligomeric lignin.
Thus, here we address the changes of Kamlet-Taft
parameters in more detail by focusing on both
α
before and after adding water. Fig. 3 shows effect of
and
β
α
values
and
β
values on the AL solubility. The starting point of each arrow
describes Kamlet-Taft parameters before adding water and the
arrowhead describes those after addition of 10 wt% of water.
Table 1 shows
in the ILs. Since solubility of AL in ILs mainly depended on the
anion species and value of ILs was also strongly influenced by
anion species, we firstly focused on a series of [C2mim] salts.
As shown in Table 1(a), value of ILs strongly influenced the
solubility of AL in ILs. However, when we focused on a series
of CF3CO2 salts, clear correlation between value and the
solubility of AL could not be observed. The CF3CO2 salts
showed value greater than 0.6, but [Mor14]CF3CO2,
β value of a series of ILs and solubility of AL
β
Considering Kamlet-Taft parameters of water (
0.14)35 into account, addition of water should decrease the
value. However,
water. For example,
α
= 1.12 and
β
=
β
β
α
value of ILs increased by the addition of
α
and values of [P4444] CF3CO2 were
β
β
0.28 and 1.06, and they were changed to 0.43 and 0.86 after
adding 10 wt% water (see arrow #9 in Fig. 3), respectively.
β
[Pip14]CF3CO2, and [P4444]CF3CO2 showed poor AL solubilisation
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 7
View Article Online
DOI: 10.1039/C7GC00626H
COMMUNICATION
Journal Name
Extraction of lignin from cedar powder
We have demonstrated that lignin solubility in ILs was induced
or improved by the addition of water. Since water addition
suppressed cellulose solubility in ILs,33 the aqueous ILs
prepared in this study are expected to be favourable for
selective extraction of lignin from biomass. Here the extraction
of lignin directly from CS has been tried (Table 2). From each
group of ILs classified based on the solubility of AL,
[C2mim]CH3O(H)PO2, [C2mim]CF3SO3, and [C2mim]BF4 were
selected as extraction solvents. Among these ILs,
[C2mim]CH3O(H)PO2 is known to dissolve cellulose in the
absence of water though others do not dissolve.20 To confirm
that addition of water reduced the solubility of cellulose in
[C2mim]CH3O(H)PO2, dissolution test of cellulose was carried
out in advance. To [C2mim]CH3O(H)PO2 containing 10 wt%
water, 0.1 wt% of cellulose (Avicel® PH101) was added and
stirred for 10 hrs. at 60 °C. The solubility was checked with
the microscope and by naked eyes. Even the added amount of
cellulose was quite small, the crystalline of cellulose was
observed suggesting the cellulose solubility in the
[C2mim]CH3O(H)PO2/water mixture is less than 0.1 wt%.
Consequently, the IL/water mixtures listed in Table 2 were
confirmed not to dissolve cellulose.
Fig. 3 Concerted effect of
α
and
β
the ILs. Arrows describe the change in
values on the AL solubility of
and values before
α
β
(starting point) and after (arrowhead) addition of 10 wt%
water. The color of number and arrow describes the solubility
for these ILs before and after addition of water (red: soluble,
black: insoluble). Each number corresponds to entry (#) 1-12
in Table 1. Others are as follows; #13: [C2OHmim][Tf2N], #14:
[P4444]N(CN)2, and #15: [P4444]CH3O(H)PO2.
Extraction was then attempted using these solvents. A
lignin extraction degree (%Elignin) of pure [C2mim]CF3SO3 and
[C2mim]BF4 was less than 2%. On the other hand,
[C2mim]CH3O(H)PO2 extracted considerable amount of lignin
with and without the presence of water, and [C2mim]CF3SO3
extracted lignin only when water was added. Induction or
improvement of lignin solubility by the addition of water was
also observed when lignin was extracted from native wood. As
a result, [C2mim]CH3O(H)PO2/water and [C2mim]CF3SO3/ water
mixtures, which are poor solvents for cellulose, extracted
7.2 % and 4.9 % of lignin from cedar powder, respectively. It
was confirmed that water addition is effective for not only
dissolution of AL but also lignin extraction from biomass.
Consequently, the IL/water mixtures were concluded to be
potential media to extract lignin from native wood without
contamination of cellulose. Of course, it is not easy to raise the
extraction yield of lignin from natural wood powder
treated under mild condition. Addition of water to some ILs
should be one of powerful methods to improve extraction of
lignin from biomass.
There is a threshold between AL soluble region and insoluble
region as shown as a broken line in Fig. 3. The arrow
(#9)started from insoluble region to soluble region.
might be a reason that solubility of AL increased after addition
of water. The IL/water mixtures with improved value may
This
α
contribute to the dissolution of AL. Also, when the CF3CO2 salts
are focused on (entry #3 and #9-12), AL dissolved in CF3CO2
salts having
Similar trend was found in the two examples, i.e.,
[C2mim]N(CN)2 (entry #5), which has higher value, dissolved
AL, and [P4444]N(CN)2 (entry #14), which has lower value, did
not dissolve AL. From these results, it was strongly suggested
that value of ILs influences AL solubility in addition to value.
Considering that [C2OHmim][Tf2N] shows poor lignin
solubilization ability in spite of its high value ( : 1.17,
0.34) 35, it was suggested that there is a critical
value to
dissolve AL, and ILs having very high value cannot dissolve AL
when their value was lower than 0.40. As shown in Fig. 3, a
α value higher than 0.5 when no water was added.
α
α
α
β
α
α
β :
β
α
Table 2 Lignin extraction degree from cedar powder by
β
IL/water mixtures.
threshold curve was depicted as the results of AL dissolution
test. This clearly shows that addition of water was eminent
only when the arrows start from AL insoluble region and
reached to AL soluble region. This can explain the effect of
water addtion to give AL dissolution ability to some ILs. Also
this can explain the enhancement of AL dissolution ability of
some ILs after addition of water. Decrease in solubility of lignin
by ILs containing excess amount of water (see Figs. 1 and 2)
Ionic liquid
[C2mim]CH3O(H)PO2
[C2mim]CH3O(H)PO2
[C2mim]CF3SO3
[C2mim]CF3SO3
[C2mim]BF4
[H2O] / wt%
Lignin extraction degree (%)
7.84 ± 0.58
0
10
0
7.23 ± 0.15
2.05 ± 0.02
10
0
4.86 ± 0.29
0.68 ± 0.11
should be attributed to the change of
threshold shown in Fig. 3.
β value lower than the
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 5 of 7
View Article Online
DOI: 10.1039/C7GC00626H
Journal Name
COMMUNICATION
15 J. H. Lora and W. G. Glasser, Journal of Polymers and the
Environment, 2002, 10, 39-48.
16 S. Kubo and J. F. Kadla, Macromolecules, 2004, 37, 6904-
6911.
17 X. Qiu, Q. Kong, M. Zhou and D. Yang, J. Phys. Chem. B, 2010,
114, 15857-15861.
18 A. Brandt, J. Gräsvik, J. P. Hallett and T. Welton, Green
Chem., 2013, 15, 550-583.
19 R. P. Swatloski , S. K. Spear , J. D. Holbrey and R. D. Rogers, J.
Am. Chem. Soc., 2002, 124 , 4974-4975.
20 Y. Fukaya, A. Sugimoto and H. Ohno, Biomacromolecules,
2006, 7, 3295–3298.
21 Y. Fukaya, K. Hayashi, M. Wada and H. Ohno, Green Chem.,
2008, 10, 44-46.
22 L. Mu, Y. Shi, L. Chen, T. Ji, R. Yuan, H. Wang and J. Zhu,
Chem. Commun., 2015, 51, 13554-13557.
23 A. Brandt, L. Chen, B. E. V. Dongen, T. Welton and J. P.
Hallett, Green Chem., 2015, 17, 5019-5034.
Conclusions
We have newly found that addition of water to ILs induces or
improve AL solubility, in spite that water is poor solvent of
biomass. Throughout the dissolution test of AL in the pure ILs,
the effect of anion on the solubility was found to be stronger
than that of cation of ILs. The AL solubility in pure ILs was
found to be the function of both proton donating and
accepting ability of ILs. Because anion structures affect
strongly on the solubility, the improvement of the solubility
triggered by water addition was observed when the ILs have
moderate
β
but increased
value (> 0.4). Addition of water decreased
value, and the improvement of
β
α
value
value
α
supported the dissolution of AL in the ILs having moderate
β
value. In other words, when ILs were mixed with water, the
polarity of ILs/water mixture changed from AL insoluble region
to soluble one. Excess amount of water further changed the
polarity of ILs outside the soluble region.
24 W. E. S. Hart, J. B. Harper and L. Aldous, Green Chem., 2015,
17, 214-218.
25 A. Guerra, I. Filpponen, L. A. Lucia, C. Saquing, S. Baumberger
and D. S. Argyropoulos, J. Agric. Food Chem., 2006, 54, 5939-
5947.
Acknowledgements
26 X. Hou, J. Xu, N. Li and M. Zong, Biotechnol. Bioeng., 2015,
112, 65-73.
27 A. P. Marques, D. V. Evtuguin, S. Magina and A. Prates, J.
Wood Chem. Technol., 2009, 29, 322-336.
28 Y. Hamada, K. Yoshida, R. Asai, S. Hayase, T. Nokami, S. Izumi
and T. Itoh, Green Chem., 2013, 15, 1863-1868.
29 A. Diop, A. H. Bouazza, C. Daneault and D. Montplaisir,
The present work was supported by Cross-ministerial
Strategic Innovation Promotion Program (SIP), Cabinet office
government of Japan (project no. 14533483). Authors
acknowledge Dr. T. Yamada of Forestry and Forest Products
Research Institute (FFPRI), Japan for preparing alkaline lignin
and cedar powder.
Bioresources, 2013, 8, 4270-4282.
30 D. Glas, C. V. Doorslaer, D. Depuydt, F. Liebner, T. Rosenau,
K. Binnemans and D. E. D. Vos, J. Chem. Technol. Biotechnol.,
2015, 90, 1821-1826.
31 Y. Wang, L. Wei, K. Li, Y. Ma, N. Ma, S. Ding, L. Wang, D.
Zhao, B. Yan, W. Wan, Q. Zhang, X. Wang, J. Wang and H. Li,
Bioresource Technology, 2014, 170, 499-505.
32 N. Phaiboonsilpa, K. Yamauchi, X. Lu and S. Saka, J. Wood
Sci., 2010, 56, 331-338.
Notes and references
1
A. J. Ragauskas, C. K. Williams, B. H. Davison, G. Britovsek, J.
Cairney, C. A. Eckert, W. J. Frederick Jr., J. P. Hallett, D. J.
Leak, C. L. Liotta, J. R. Mielenz, R. Murphy, R. Templer and T.
Tschaplinski, Science, 2006, 311, 484-489.
33 M. Mazza, D. Catana, C. V. Garcia and C. Cecutti, Cellulose,
2009, 16, 207-215.
34 V. M. Roberts, V. Stein, T. Reiner, A. Lemonidou, X. Li and J.
A. Lercher, Chemistry, 2011, 17, 5939-5948.
35 C. Chiappe, C. S. Pomelli and S. Rajamani, J. Phys. Chem. B,
2011, 115, 9653-9661.
2
3
S. Rastogi and U. N. Dwivedi, Plant Science, 2008, 174, 264-
277.
S. V. D. Bosch, W. Schutyser, R. Vanholme, T. Driessen, S. F.
Koelewijn, T. Renders, B. D. Meester, W. J. J. Huijgen, W.
Dehaen, C. M. Courtin, B. Lagrain, W. Boerjanbc and B. F.
Sels, Energy Environ. Sci., 2015, 8, 1748- 1763.
Z. Strassberger, P. Prinsen, F. V. D. Klis, D. S. V. Es, S. Tanasea
and G. Rothenberg, Green Chem., 2015, 17, 325-334.
4
5
6
R. Rinaldi, Angew. Chem. Int. Ed., 2014, 53, 8559-8560.
E. M. Karp, M. G. Resch, B. S. Donohoe, P. N. Ciesielski, M. H.
O’Brien, J. E. Nill, A. Mittal, M. J. Biddy and G. T. Beckham,
ACS Sustainable Chem. Eng., 2015, 3, 1479-1491.
7
8
9
K. Dussan, B. Girisut, D. Haverty, J. J. Leahy and M. H. B.
Hayes, Carbohydrate Polymers, 2014, 111, 374-384.
S. M. Hick, C. Griebel, D. T. Restrepo, J. H. Truitt, E. J. Buker,
C. Bylda and R. G. Blair, Green Chem., 2010, 12, 468-474.
J. Li, G. Henriksson and G. Gellerstedt, Bioresource
Technology, 2007, 98, 3061-3068.
10 M. Sasaki, T. Adschiri and K. Arai, Bioresource Technology,
2003, 86, 301-304.
11 A. Jönsson and O. Wallberg, Desalination, 2009, 237, 254-
267.
12 A. Toledano, L. Serrano, A. Garcia, I. Mondragon and J.
Labidi, Chemical Engineering Journal, 2010, 157, 93-99.
13 A. Vishtal and A. Kraslawski, Bioresources, 2011, 6, 3547-
3568.
14 A. V. Ellis , M. A. Wilson and P. Forster, Ind. Eng. Chem. Res.,
2002, 41, 6493-6502.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Green Chemistry
Page 6 of 7
View Article Online
DOI: 10.1039/C7GC00626H
Kamlet-Taft parameters of ionic liquid/water mixtures are the function of added water concentration.
As water concentration increases, proton accepting ability of polar ionic liquids decreases but proton
donating ability increases, respectively. This is the reason why some ionic liquids, that have no
lignin dissolution ability, get lignin dissolution ability by the addition of suitable amount of water.

Page 7 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C7GC00626H
162x154mm (150 x 150 DPI)