Quantitative glucose release from softwood after pretreatment with low-cost ionic liquids

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: F. J. Gschwend,

C. L. Chambon, M. Biedka, A. Brandt, P. Fennell and J. Hallett, Green Chem., 2019, DOI:

1

0.1039/C8GC02155D.

Volume 18 Number

7

April 2016 Pages 1821–2242

This is an Accepted Manuscript, which has been through the

Royal Society of Chemistry peer review process and has been

accepted for publication.

Green

Chemistry

Cutting-edge research for a greener sustainable future

www.rsc.org/greenchem

Accepted Manuscripts are published online shortly after

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

standar d 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

View Article Online

DOI: 10.1039/C8GC02155D

Page 1 of 13

Green Chemistry

Journal Name

RSCPublishing

ARTICLE

Quantitative Glucose Release from Softwood after

Pretreatment with Low-cost Ionic Liquids

Cite this: DOI: 10.1039/x0xx00000x

Florence J. V. Gschwend, Clementine L. Chambon, Marius Biedka, Agnieszka

Brandt-Talbot, Paul S. Fennell and Jason P. Hallett*

Received 00th January 2012,

Accepted 00th January 2012

Softwood is an abundantly available feedstock for the bio-based industry, however, achieving

cost-effective sugar release is particularly challenging owing to its guaiacyl-only lignin. Here,

we report the highly effective pretreatment of the softwood pine (Pinus sylvestris) using

ionoSolv pretreatment, a novel ionic liquid-based lignocellulose fractionation technology.

Three protic, low-cost ionic liquids, 1-butylimidazolium hydrogen sulfate, triethylammonium

hydrogen sulfate and N,N-dimethylbutylammonium hydrogen sulfate, were used to fractionate

the biomass into a carbohydrate-rich pulp and a lignin. The carbohydrate-rich pulp was

hydrolysed into fermentable sugars by enzymatic saccharification. Under the most successful

pretreatment conditions, quantitative glucose release from the pulp was achieved, which

equates to a projected glucose release of 464 mg per gram of pine wood entering the process.

We further intensified the process by increasing the solid to solvent ratio up to 1:2 g/g while

maintaining saccharification yields of 75% of the theoretical maximum. We also demonstrate

DOI: 10.1039/x0xx00000x

www.rsc.org/

4

for the first time that N,N-dimethylbutylammonium hydrogen sulfate, [DMBA][HSO ] is an

excellent low-cost pretreatment solvent, surpassing the pretreatment effectiveness of its

symmetrically substituted analogue triethylammonium hydrogen sulfate. This shows that

ionoSolv pretreatment with protic hydrogen sulfate ionic liquids is a truly feedstock-

independent pretreatment option, further increasing the commercial potential of this

pretreatment technology.

competitiveness of bio-derived products compared to cheap,

highly optimised petroleum-derived fuels and chemicals.²^,⁴To

Introduction

Bioenergy and biorefining research has attracted widespread minimize unsustainable land use changes associated with

attention in recent years as many countries seek to minimise feedstock production for biorefining, emphasis has shifted

their reliance on oil imports, reduce their carbon emissions and towards utilisation of lignocellulosic biomass, which refers to

boost their agricultural and forestry sectors. Petroleum is the woody and thus inedible parts of plants. Fuels and

currently relied upon for the production of the majority of the chemicals produced from lignocellulose are referred to as

1

world’s liquid fuels, plastics, solvents and chemicals. A shift second-generation; promising lignocellulosic crops are

towards the use of biomass instead of petroleum will require dedicated energy crops (i.e. Miscanthus and short-rotation

significant investment in the development of novel process coppice willows), agricultural residues (corn stover, sugarcane

technologies.²

bagasse and wheat straw) or forestry residues, the latter often

3

Considering the importance of liquid fuels worldwide within being composed of softwoods such as pine and fir. Although

the transportation sector, there are increasing opportunities for lignocellulose is an abundant and relatively inexpensive source

biofuels to be incorporated into the energy mix. Biofuels can of sugars, its greater structural complexity means that the

contribute towards energy security, if produced sustainably, sugars are much harder to isolate than sucrose or starch. In

however, a number of factors currently limit expansion. These order to release sugars, a pretreatment step is required to

include concerns surrounding competition for land with food increase accessibility of cellulose prior to hydrolysis of the

production, or with endangered habitats with high carbon- sugars contained within, a process that adds substantial costs.⁵

storage capacity.³A major barrier is also the economic Negative effects on downstream processes by side-products

This journal is © The Royal Society of Chemistry 2013

J. Name., 2013, 00, 1-3 | 1

View Article Online

DOI: 10.1039/C8GC02155D

Green Chemistry

Page 2 of 13

Journal Name

ARTICLE

8

generated during pretreatment pose further challenges. These experiments. Softwood is produced sustainably for timber and

issues currently present a technical and economic obstacle to paper production and widely available as a forestry residue, in

establishing cellulosic sugar based biorefineries.

the form of sawdust at timber and pulp mills, or as construction

Ionic liquid pretreatment is a comparatively new biomass waste wood.²⁵According to NNFCC Bioeconomy Consultants,

deconstruction approach. Two strategies during the ionic liquid around 1.3 million tonnes of softwood forest waste arise in the

pretreatment of lignocellulosic biomass are being followed: UK annually, which can be removed from forests sustainably at

decrystallization of cellulose⁶^,⁷and extraction of lignin (i.e. a cost of between £18-50/dry tonne vs. around 140 thousand

ionoSolv pretreatment).⁸^,⁹The Dissolution pretreatment option tonnes of Miscanthus produced in the UK (including 16%

relies on ionic liquids with strongly hydrogen-bond basic moisture) at a cost of £45-70/tonne.²⁶An advantage of

anions, such as 1-ethyl-3-methylimidazolium acetate softwood is the high content of hexoses (Figure 1), due to the

[

EMim][OAc], which dissolve cellulose in the absence of glucomannan dominated hemicellulose.²⁷Hexose sugars are

water.¹⁰Regenerated cellulose and hemicellulose exhibit a readily fermented by conventional yeasts,²⁸while many

better and faster digestibility (ca. 50 times higher enzymatic fermentative organisms are not adapted to the conversion of

hydrolysis rate) due to lower crystallinity¹¹^,¹²and enlarged pentose sugars (xylose and arabinose), which make up the

surface area, but these ionic liquids suffer from low thermal majority of hemicellulose sugars in grasses and hardwoods.²⁷

stability (limiting their recyclability),¹³requirement for dry Softwoods are known to be more recalcitrant than grasses and

conditions, and high solvent cost.¹⁴The ionoSolv pretreatment hardwoods due to a higher lignin content (up to 30%)²⁷and due

extracts the majority of lignin from biomass such as to the lignin consisting predominantly of guaiacyl (G) units

Miscanthus⁸^,¹⁵^,¹⁶sugarcane bagasse¹⁷and willow¹⁸in the (95%).²⁹Guaiacyl units result in a higher content of biphenyls

presence of 10-40 wt% water. Although the cellulose is still and diphenyl ethers in the lignin,⁸and more easily form

crystalline, saccharification is enhanced and accelerated up to condensed structures during processing, therefore presenting a

4

0 times compared to untreated biomass due to increased greater challenge to delignify, creating a barrier to quantitative

surface area and the removal of lignin. The ionoSolv sugar release and requiring high (Costly) enzyme loadings for

pretreatment is therefore in its function similar to Organosolv saccharification.³⁰Due to this, low-cost aqueous pretreatment

pretreatment.⁸^,¹⁹^,²⁰The extracted lignin can be recovered via such as steam explosion³¹and dilute acid³²are largely

addition of water as an anti-solvent, while the cellulose can be ineffective in pretreatment of this recalcitrant feedstock. Better

hydrolysed to glucose via enzymatic saccharification and used results can be obtained with Organosolv³³and alkaline

in subsequent fermentations or chemical transformations. peroxide³⁴pretreatments, however high capital and chemical

During ionoSolv pretreatment, β-O-4’ linkages in the lignin are recovery cost limit their applicability.

broken, leading to fragmentation;²¹however, lignin A limited number of studies have applied ionic liquid in

condensation reactions may also occur. It has been discovered softwood pretreatment. A study using dissolution pretreatment

that protic ILs, such as 1-butylimidazolium hydrogen sulfate with the ionic liquid 1-butyl-3-methylimidazolium chloride

[

HBim][HSO

4

]

and triethylammonium hydrogen sulfate [BMim]Cl has shown that a highly digestible pulp can be

[

TEA][HSO

4

]¹⁶^,²²demonstrate similar efficacy as their obtained from pine wood chips with a glucose yield of around

dialkylimidazolium counterparts,²³and the alkylammonium IL 78%.³⁵Cox et al. used the protic ionic liquid

[TEA][HSO4] can be recycled multiple times with a slight 1-methylimidazolium chloride [HMim]Cl, obtaining up to 50%

increase in saccharification yield observed upon recycling.16 glucose release from pine chips.³⁶Both studies, however,

This is significant, as protic ionic liquids can be prepared via employed low, economically unattractive biomass to solvent

one-step acid-base reactions using readily available amines and ratios of 1:20 and ca. 3:100 g/g, respectively.

mineral acids. A recent study has suggested prices of $1.24 kg^-¹

for triethylammonium hydrogen sulfate and between $2.96-

₅_.₈₈_k_g_-1 for 1-methylimidazolium hydrogen sulfate, if

1.3

0.8

$

synthesised on a bulk scale.²⁴This compares well to pricing for

4

3.4

13.3

common organic solvents such as acetone or ethyl acetate,

27.6

80%

4.5

-1

which cost between $1.30-$1.40 kg . Recently, we showed that

the pretreatment of Miscanthus with [TEA][HSO ] can be

4

.5 4.6

carried out at 180°C for 15 min without any yield penalty,

leading to commercially relevant process intensification.²²We

0

%

20%

40%

60%

100%

4

have further demonstrated that [TEA][HSO ] can be re-used at

least 4 times for pretreatment of Miscanthus while maintaining

Glucan

ASL

Mannan

AIL

Xylan

Ash

Arabinan

Extractives

high saccharification yield and no ionic liquid degradation was

detected through proton NMR.¹⁶

Figure 1 Composition of pine wood used in this study. ASL: acid-soluble lignin,

AIL, acid insoluble lignin.

_T_h_u_s_f_a_r_,_M_i_s_c_a_n_t_h_u_s₁6,22 sugarcane bagasse¹⁷and willow¹⁸

have been the main feedstocks investigated for deconstruction

and fractionation with ionoSolv ionic liquids, while softwoods

have received little attention apart from preliminary

This study investigates the application of protic, hydrogen

sulfate based ionic liquids for the fractionation of pine, a

This journal is © The Royal Society of Chemistry 2012

J. Name., 2012, 00, 1-3 | 2

View Article Online

DOI: 10.1039/C8GC02155D

Page 3 of 13

Journal Name

Green Chemistry

ARTICLE

commonly grown softwood with wide geographical

abundance.³⁷

We optimise pretreatment conditions

temperature and time) according to a bench-scale protocol

1

20°C

(

100

developed in our laboratory,¹⁵applying the protic ionic liquid

N-butylimidazolium hydrogen sulfate. Enzymatic glucose

release was used as the key indicator. We also analysed the

composition of the cellulose-rich pulp and chemical

characteristics of the isolated lignin. We then applied two low-

cost alkylammonium hydrogen sulfate ionic liquids at the

optimised conditions. For the first time, an asymmetric

trialkylammonium hydrogen sulfate ionic liquid was used for

ionoSolv fractionation, and its effectiveness was compared with

the alkylimidazolium and symmetric tirethylammonium

analogues. The ions making up the three ILs used in this study

are displayed in Figure 2.

8

0

60

4

0

20

0

2

4

6

8

Hours of Pretreatment

1

50°C

1

00

8

6

0

N

NH

40

HSO₄

N

NH

2

0

H

Figure 2 Structures of the ionic liquid ions used in this study: the hydrogen

0

+

sulfate anion, and the 1-butylimidazolium, [HBim] , triethylammonium, [TEA] ,

0

2

4

6

8

+

and N,N-dimethylbutylammonium, [DMBA] , cations.

Hours of Pretreatment

1

70°C

1

00

Results and discussion

8

0

EFFECT OF TEMPERATURE AND TIME ON PRETREATMENT

WITH [HBIM][HSO

4

]

60

40

Fractionation effectiveness and enzymatic saccharification yield

A set of experiments was carried out using the protic ionic

2

0

liquid 1-butylimidazolium hydrogen sulfate [HBim][HSO

three different oven temperatures (120, 150 and 170°C) with a

:10 g/g biomass to solvent ratio. As we discussed in our study

on process intensification of Miscanthus fractionation using

triethylammonium hydrogen sulfate [TEA][HSO

],²²the

4

] at

0

1

2

3

4

1

Hours of Pretreatment

4

Glucan recovery

Delignification

designated reaction temperature inside the pretreatment vessel

is only reached after around 30 min. This should be borne in

mind when interpreting results for pretreatment times of 30 min

or less.

Lignin precipitate

Saccharification yield

Hemicellulose removal

Figure 3 shows how a number of indicators for pretreatment

and fractionation effectiveness perform over time. The glucan

recovery, delignification and (non-glucan) hemicellulose

removal were derived by combining compositional analysis

Figure 3 Key indicators of fractionation effectiveness for pine wood

pretreated at 120°C, 150°C and 170°C with [HC im][HSO ] containing 20

wt% water. The biomass to solvent ratio was 1:10 g/g

4

data and pulp yields; the precipitated lignin yield was since we observed high glucose release when performing

determined gravimetrically. The enzymatic glucose release additional experiments with wet pulp, which are detailed

(

saccharification yield) was determined for air-dried pine pulps. towards the end of the manuscript. After the initial decrease,

The saccharification yield is a key performance indicator, as saccharification yields increased beyond that released from

glucose is a key substrate for fermentations or chemical untreated biomass for all investigated temperatures. For 120°C,

transformations producing bio-based chemicals and fuels.

the saccharification yield did not reach a peak within the

For the saccharification yield, we observed an initial decrease timeframe studied, while for experiments at 150 and 170C,

compared to untreated pine at all three temperatures. We there was a peak saccharification yield at 60 and 30 min,

attribute this to hornification (irreversible pore collapse) respectively. The highest observed glucose releases were 44, 62

occurring during the air-drying of the pulp after washing,³⁸and 71% for 120, 150 and 170°C, respectively, showing that a

This journal is © The Royal Society of Chemistry 2012

J. Name., 2012, 00, 1-3 | 3

View Article Online

DOI: 10.1039/C8GC02155D

Green Chemistry

Page 4 of 13

Journal Name

ARTICLE

higher pretreatment temperature is essential for effective industrial-scale protocol (we anticipate a washing step with

enzymatic cellulose hydrolysis. The peak saccharification recycled ionic liquid instead) and less redeposition is therefore

yields occurred at similar pretreatment conditions identified for expected under scaled-up conditions. An extensive study of

Miscanthus,²²sugarcane bagasse¹⁷and willow¹⁸pretreatment ionoSolv softwood pretreatment up to the 200 L scale has been

with [TEA][HSO

4

].

performed and will be reported in the near future.

Peak delignification was 79% at 150°C and 81% at 170°C, and We further note that no minimum for the lignin content was

it appeared to occur slightly later than peak saccharification. found within the studied timeframe at 120°C for pine, while a

We also observed that saccharification yield and lignin removal minimum can be detected for other feedstock types. For pine,

correlated strongly, as can be seen from Figure 4. A delignification and saccharification yield was limited to 66%

relationship

saccharification yield was reported previously for saccharification yield for Miscanthus pretreated with

Miscanthus.¹⁶^,²²

[TEA][HSO ], showing that softwood requires higher

between

delignification

and

enzymatic and 44% after 8 h compared to a 88% delignification and 77%

4

temperatures in order to achieve good pretreatment results.¹⁶

The reason for this may be that lignin extraction is facilitated

above the glass transition temperature of lignin (thought to be

in the range 130-150°C).⁴¹We hypothesise that fast extraction

from the cellulose pulp is particularly beneficial for softwood

delignification, as guaiacyl-rich lignin is prone to forming

stable crosslinks in acidic systems via condensation reactions.⁴²

Glucan recoveries were fairly constant under mild conditions

8

7

6

5

4

3

2

1

0

(i.e. at 120°C), while hemicellulose was removed over time.

For 120°C, we observed that hemicellulose removal from pine

was faster than hemicellulose removal from Miscanthus using

0

20

40

60

80

100

[

TEA][HSO

4

],¹⁶with 64% of hemicelluloses removed in the

Delignification (%)

first hour of pretreatment compared to 44% in the case of

Miscanthus. High temperatures accelerated hemicellulose

removal. Near-quantitative hemicellulose removal was

Figure 4 Correlation of enzymatic glucose release and delignification of pine after

pretreatment with [HC im][HSO ] with a water content of 20 wt% and a pine

4

wood to solvent ratio of 1:10 g/g at different temperatures and times. achieved after 4 h and 45 min at 150 and 170°C, respectively,

Percentage of the theoretical maximum according to compositional analysis is

shown.

which is similar to what was observed for Miscanthus

pretreated with [TEA][HSO

4

].²²The recovery and valorisation

of the dissolved hemicellulose portion from ionoSolv solutions

remains a challenge. One suggested option is to produce

furfural.¹⁶

At 150 and 170°C, the amount of lignin associated with the

pulp increased after reaching a minimum (2 h at 150°C and

3

0/45 min at 170°C). This has been observed in the past for

For the temperatures above 120°C, we observed that

pretreatment effectiveness declined past the optimum point,

which we attribute to reduced glucan recovery and deposition

of condensed lignin and pseudo-lignin on to the surface of the

cellulose fibrils. This was confirmed by compositional analysis

of the pulps (numerical values can be found in Table S1 in the

ESI). In an extreme case, the glucan recovery dropped to zero

after 4 h of pretreatment at 170°C. We note that glucan

appeared to be less stable in this study compared to Miscanthus

pretreatment of Miscanthus with [TEA][HSO ] at temperatures

4

of 150-180°C.²²The increase in the amount of lignin present in

the pulp at the later stages of pretreatment has been attributed to

both condensation reactions within lignin fragments and the

formation of pseudo-lignin from hemicellulose which

contribute to the formation of high molecular weight substances

which can precipitate onto the pulp surface.³⁹While the

compositional analysis technique fails to distinguish between

actual lignin and pseudo-lignin, formation of the latter is

strongly suspected under conditions where the lignin precipitate

exceeds the measured delignification (e.g. after more than 1 h at

pretreatment in [TEA][HSO

nearly 100% at 150°C and 4 h,²²compared to 70% glucan

recovery after 4 h of pretreatment of pine with [HBim][HSO ].

4

], where glucan recovery was

4

1

70°C). Evidence for condensation reactions was found when

It is currently unclear if the differences in cellulose and

hemicellulose stability are due to the nature of the feedstock or

the ionic liquid. An initial decrease in glucan recovery in the

pulp has been attributed to removal of glucose containing

hemicelluloses, such as galactoglucomannans and xyloglucans,

rather than degradation of cellulose.⁴³Galactoglucomannans

constitute up to 15% of softwood.⁴⁴

analysing the precipitated lignin, which is discussed below.

The re-precipitation of condensed lignin and also that of

pseudo-lignin on to the cellulose surface are thought to have a

negative effect on saccharification yields and kinetics by

making the cellulose substrate less accessible.⁴⁰It should

further be noted that the work-up procedure used here involves

diluting the IL with ethanol after pretreatment to facilitate its

separation from the pulp. Visual observations suggested that

ethanol-induced lignin precipitation was responsible for some

of the lignin reprecipitation at prolonged pretreatment times.

We note that dilution with ethanol is unlikely to be part of an

Lignin characterisation

As was shown in the previous section, there is a clear link

between residual lignin content in the pulp, and saccharification

This journal is © The Royal Society of Chemistry 2012

J. Name., 2012, 00, 1-3 | 4

View Article Online

DOI: 10.1039/C8GC02155D

Page 5 of 13

Journal Name

Green Chemistry

ARTICLE

yields (Figure 4). In order to improve the economics of

cellulosic biorefineries, not only the cellulose/sugar yield needs

to be optimised, but also the characteristics of the lignin. We

therefore analysed the isolated lignins for their subunit

composition and linkages and the molecular weight to gain

insight into the reactions taking place. Pine lignin (and more

generally softwood lignin) consists predominantly of guaiacyl

(G) units (95%) and around 45-50 β-O-4’ linkages per 100

aromatic rings.²⁹The second most abundant linkage in

softwood lignin is the phenylcoumaran (β-5’) linkage with

around 10-13 linkages per 100 aromatic units. In smaller

numbers, resinol (β- β’) and diarylpropane (β-1’) linkages are

also present.⁴⁵^,⁴⁶Figure 5 shows the most important linkages

and subunits in pine lignin.

Figure 6 shows the aromatic and the oxygenated regions of a

representative HSQC NMR spectrum for one of the isolated

pine lignins. Peaks for the three unsubstituted positions of the

guaiacyl ring as well as certain linkages were assigned. We

note that there are a number of peaks in the aromatic region of

the spectrum which are currently unassigned, as they do not

match any of the commonly found structures in ball-milled

lignin. They probably correspond to new structures formed

during the ionic liquid extraction. We also observed a peak at

4

.2/67 ppm, which we assign to the plasticiser bis(2-ethylhexyl)

phthalate (DEHP). It has been observed in a previous study¹⁶

and is presumed to have been leached from the seals of the

pressure tubes used for heating the biomass with the ionic

liquid and subsequently precipitated with the lignin fraction

during antisolvent addition.

Figure 6 HSQC NMR spectra of pine lignin isolated after extraction with

[HC

water content of 20 wt%. The side chain region (top) and aromatic region

bottom) are shown. PL is plasticizer. Two signals for residual butylimidazolium

4 4

im][HSO ] at 170°C for 30 min with a biomass to solvent ratio 1:10 g/g and a

(

are marked in red. Grey peaks could not be assigned.

RO



O

The pulse sequence used in these experiments only gives semi-

quantitative information, since equilibration of the 13_C

excitation is incomplete within the programmed relaxation time



5



'

HO









HO



'

O







'



'

'

(in order to achieve manageable acquisition times), and carbon

O

nuclei will relax at different rates in different chemical

environments. However, the observed peak volume is linear

with respect to the concentration of the analyte, so time course

trends can be established with a suitable internal standard. It

A

B

C



-aryl ether (-O-4')

resinol (-')

phenylcoumaran (-5')

2

has been suggested in previous literature that the G signal can

be used as such an internal standard in the case of softwoods, as

it is not thought to participate in condensation reactions or

overlap with signals of degradation products.⁴⁵It should

therefore be representative of the total number of aromatic units

OH

1

'



6



2



OH

5

O

in the lignin. However, the G

undergo chemical modification, leading to a G2,cond peak, hence

the sum of G and G2,cond is used here as a reference integral.

2 6 5

signal shifts if G or G sites

O

2

D

G

With these assumptions, we compared the signal intensities for

the four ether linkages shown in Figure 5 and the different

positions of the guaiacyl unit found in the precipitated lignin, in

order to discuss characteristics of the isolated lignins, and lignin

reactivity more generally.

diarylpropane (-1')

guaiacyl

Figure 5 The most prominent ether bonds and lignin subunit in pine lignin.

Figure 7 shows the relative HSQC volume integrals for pine

lignin isolated after pretreatment for 1 h at 120, 150 and 170°C.

It can be seen that the majority of β-O-4’ ether linkages (45-

This journal is © The Royal Society of Chemistry 2012

J. Name., 2012, 00, 1-3 | 5

View Article Online

DOI: 10.1039/C8GC02155D

Green Chemistry

Page 6 of 13

Journal Name

ARTICLE

5

0%), the most abundant lignin linkages in pine wood,⁴⁵were

broken after pretreatment for 1 h. The data suggest that the

ether bonds contained in the less abundant β-β’ and β-5’

linkages break at a slower rate, which has been observed

previously.²²Similarly, the aromatic ring signals provided

evidence for substitution reactions occurring on the aromatic

rings (lignin condensation). The degree of condensation was

higher at high pretreatment temperatures, as evidenced by the

80

6

4

0

20

0

lower G

for the 150°C lignin, and even more so for the 170°C lignin.

We note that there was an unexpected increase in the G signal

6 2

and G signal intensities and the higher G2.cond signal

5

intensity. We have preliminary evidence that this is due to

carbohydrate-derived degradation products which are generated

under acidic conditions and precipitate with the lignin. We will

provide more data on this topic in a future publication.

4

h 120°C

1 h 150°C

0.5 h 170°C

Figure 8 Abundance ether linkages and unsubstituted aromatic ring sites in lignin

precipitates obtained after pretreatment of pine wood with [HBim][HSO ] with

0 wt% water. The lignin and saccharification yield are shown for reference. The

4

2

lignins selected here were similar in composition, while indicators of

pretreatment effectiveness were markedly different.

8

7

6

5

4

3

2

1

0

EFFECT

OF

BIOMASS LOADING

ON

PRETREATMENT

EFFECTIVENESS

Lignocellulose pretreatment is a capital-intensive process, with

the pretreatment reactor(s) expected to represent ca. 20% of the

capital expenditure (CAPEX) in a typical cellulosic ethanol

plant.⁴⁷^,⁴⁸Since the pretreatment reactor size and also solvent

cost will scale approximately inversely with solids loading

β-β' β-O-4' β-1'

β-5'

G6

G5

G2

cond

G2

(

more precisely with total volume), a higher solids loading will

intensify the process and decrease CAPEX by approximately

0% when doubled, according to standard power laws

exponent 0.7) for economies of scale.²²In order to improve the

1

h 120°C

1 h 150°C

1 h 170°C

4

(

Figure 7 Abundance of ether linkages and C-H

isolated pine lignin, obtained after pretreatment with [HBim][HSO

n

sites on the guaiacyl ring of

4

] with 20 wt%

economic viability of ionoSolv pretreatment of pine wood, high

solids loadings are therefore important.⁴⁹

water for 1 h.

We thus assessed the pretreatment efficacy for pine at loadings

ranging from 5 to 50 wt%, corresponding to biomass to solvent

ratios from 1:20 to 1:2 g/g. These experiments were carried out

using the optimal conditions for glucose release from the pulp

We also compared the characteristics of the lignin isolated at

the optimum pretreatment conditions. Figure 8 shows the

relative size of the ether linkage and guaiacyl ring signals for

lignins isolated after 0.5 h at 170°C, 1 h at 150°C and 4 h at

identified for [HBim][HSO

shows the pulp, lignin and saccharification yields

saccharification conducted after air-drying of the pulps) as a

4

] (170°C for 30 min). Figure 9

1

20°C, as well as the corresponding lignin precipitate and

saccharification yield of the pulp (as a percentage of the

maximum possible). The data show that these lignins had a

similar degrees of condensation and quantities of unhydrolysed

ether linkages, while lignin and saccharification yields were

substantially different. We have previously shown that lignin

isolated from Miscanthus at optimum conditions using

(

function of the biomass loading. Pulp yields increased from

around 41% to 56% when increasing the loading from 5 to 50

wt%. Lignin yields remained stable at around 55% for the 5-

25% solid loading range, while for the 35 and 50 wt% loadings,

_]_a_r_e_d_i_f_f_e_r_e_n_t_i_n_c_h_e_m_i_c_a_l_c_h_a_r_a_c_t_e_r_i_s_t_i_c_s_.₂2 Here,

a drop in the lignin yield to around 30% was observed. The

saccharification yield was highest at the lowest loading, giving

[TEA][HSO

4

we observe that lignin extraction and yield can be increased

with temperature without altering the degree of condensation

and the degree of hydrolysis in the precipitated lignin. This

could be due to the different compositions of grass and

softwood lignins.

7

5

8% of the theoretical yield, decreasing to below 40% for the

0 wt% pine wood loading.

This journal is © The Royal Society of Chemistry 2012

J. Name., 2012, 00, 1-3 | 6

View Article Online

DOI: 10.1039/C8GC02155D

Page 7 of 13

Journal Name

Green Chemistry

ARTICLE

lower M

w

at higher loadings. This is consistent with the

apparent trend towards more ether cleavage with increasing

biomass loading. Especially the decrease in the PDI is thought

to stem from an upper cut-off for M during ethanol dilution at

w

high loadings, resulting in a narrower range of molecular

weights in the isolated lignin.

These findings suggest that delignification and the structure of

the extracted lignin are not altered in a significant way at higher

loadings, but lignin yield and molecular weight of the isolated

lignin is. The lignin and saccharification yield, and the pulp

recovery, may be improved, and higher loading allowed with

an adapted washing protocol that avoids re-precipitation and/or

removes re-precipitated lignin from the pulp surface.

80

70

60

50

40

30

20

10

0

10

20

30

40

50

Biomass Loading (wt%)

Pulp recovered

Lignin precipitate

Saccharification yield

9

0

Figure 9 Effect of biomass loading on pulp yield, lignin yield and glucose release

from the pulp via enzymatic saccharification after pretreatment of pine with

80

7

6

5

4

3

2

1

0

[

4

HBim][HSO ] (20 wt% water) for 30 min at 170°C.

The increase in pulp yield and the decrease in lignin yields with

higher loading could be due to limitations of particle wetting in

the ionic liquid solution. It is also possible that the lignin was

extracted and precipitated during the pulp washing with

ethanol, discussed in more detail below.

We also investigated how lignin properties are affected by

increasing the biomass loading. Figure 10 shows the HSQC

NMR signal intensities, as well as molar mass of the lignins as

a function of biomass loading. The HSQC NMR analysis

showed only small changes in the chemical functionality of the

recovered lignins with increasing biomass loading. It appears

that the ether linkage content in the isolated lignin decreased

slightly with increased loadings, and the degree of condensation

and pseudo-lignin content also rose, which could be due to

increased concentration of dissolved lignin fragments and

hemicellulose in the ionic liquid solution. The observed

differences are small, however, and they may not be significant.

Overall, the compositions of the lignins isolated at various

loadings were broadly similar.

β-β' β-O-4' β-1'

10%

β-5'

15%

G2

cond

G2

G5

50%

G6

5

%

25%

35%

1

0000

6

4

2

0

8

6

000

4000

2

000

0

20

40

60

Biomass Loading (%)

n w

The GPC data demonstrate a decrease in M and M with

higher loading, although the values found for the 15 and 25

wt% loading experiments were inconsistent with the trend.

Furthermore, the PDI of the isolated lignin was lower at higher

loadings. As mentioned earlier, the observed differences may

Mn

Mw

PDI

Figure 10 (Top) Abundance of chemical functionalities in isolated pine lignin as a

function of biomass loading according to HSQC NMR spectroscopy. Signal

intensities are relative to 100

2

G +G2,cond. (Bottom) Molar masses and

be due to the pulp isolation method (employing ethanol polydispersity of recovered lignins as a function of biomass loading. Pine was

4

pretreated with [HBim][HSO ] (20 wt% water) for 30 min at 170°C.

washing), resulting in a bias in the fraction recovered rather

than the lignin structure being affected by the higher loading

directly. This is supported by the fact that sulfate based ionic Effect of pulp drying and hornification on saccharification yields

liquids have been shown to dissolve up to 70 wt% lignin⁵⁰and

it is therefore unlikely that we were witnessing saturation even

be subjected to enzymatic hydrolysis directly after washing,

at the highest biomass loadings. However, ethanol has a much

lower lignin solubility,⁵¹and so its addition is likely to

laboratory procedure in order to facilitate sample handling).

precipitate larger fragments out of solution during the washing

step. Since the solubility of polymers of equivalent chemical

hornification of pretreated lignocellulose which negatively

functionality is governed by molecular size, we expect that the

In an industrial process, the cellulose-rich pulp is expected to

rather than undergoing an air-drying step (which is part of our

However, we note that there is evidence that air-drying leads to

affects enzymatic saccharification _y_i_e_l_d_s_,38 hence we

cut-off for larger fragments in ethanol would be at slightly

investigated whether omitting the air-drying would improve

This journal is © The Royal Society of Chemistry 2012

J. Name., 2012, 00, 1-3 | 7

View Article Online

DOI: 10.1039/C8GC02155D

Green Chemistry

Page 8 of 13

Journal Name

ARTICLE

glucose release from pine pulps. For this, pulp samples were outcome than a more expensive alkylimdiazolium hydrogen

submerged in water directly after Soxhlet extraction with sulfate. Lignin recovery correlated well with saccharification

ethanol. Moisture contents of wet pulps obtained after solvent yields. The highest lignin recovery was observed for

exchange were around 90 wt%. Wet saccharification was [DMBA][HSO

carried out for pulps obtained at 10 or 50 wt% loading (1:10 saccharification yield (30 and 36%, respectively) were obtained

and 1:2 g/g biomass to solvent ratio), using the optimised when using [TEA][HSO ]. This was less than half of the yields

pretreatment conditions of 30 min at 170°C for [HBim][HSO ]. achieved by the best-performing [DMBA][HSO ].

The results in Table 1 show that the sugar release from wet [TEA][HSO ] has previously been shown to effectively

4

](72%), while the lowest lignin recovery and

4

pulps was substantially higher. At 10% loading, we observed delignify Miscanthus,¹⁶sugarcane bagasse¹⁷and willow¹⁸

quantitative glucose release from the wet pulp, while at 50% biomass, resulting in saccharification yields of up to 80% from

loading, 75% of the glucose was released, representing an air-dried pulps,¹⁴^,¹⁶although slightly higher yields at optimised

increase of 57 and 120% vs. the dried pulps, respectively. This conditions have been typically observed for imidazolium based

represents a significant improvement. Even with the lower yield hydrogen sulfate ILs (up to 90%).²³It is unclear at present why

at 50% biomass loading, we estimate the reduction in reactor [TEA][HSO

size would reduce CAPEX per tonne of glucose obtained by [HBim][HSO

4

]

was so drastically outperformed by

] and [DMBA][HSO ] in this case. We note that

4

5

7%.

the order of fractionation performance mirrors how fast the

three ionic liquids hydrolyse β-O-4 linkages, as measured by

Table 1 Saccharification yield obtained from air-dried and wet pine pulps. Pine was

pretreated at 170°C for 30 min with a solid to solvent ratio of 1:10 and 1:2 g/g in

Gregorio et al.⁵³We also note that [DMBA][HSO

] and

4

TEA][HSO ] have the same molar mass and it is therefore

4

[

4

HBim][HSO ].

unlikely that the difference in performance is linked to an effect

of molar ratio of ionic liquid to water or biomass. Work on

correlating the effect of ionic liquid cation substitution pattern

with pretreatment efficacy is currently underway and will be

presented in due course.

Saccharification yield

Loading

0%

with air drying

without air drying

102.2±1.9%

1

5

64.8±3.5%

34.4±3.2%

74.9±2.9%

SELECTION OF IONIC LIQUID

The imidazolium-based ionic liquid [HBim][HSO ] can be

4

produced at relatively low-cost compared to many imidazolium

ILs, due to being a protic IL that can be synthesised from

inexpensive sulfuric acid and the imidazole precursor in one

step. However, alkylammmonium hydrogen sulfates would be

more cost-effective, as the 1-butylimidazole precursor is still

fairly expensive. Hence we tested two ILs made from low-cost

amines, triethylammonium hydrogen sulfate, [TEA][HSO

N,N-dimethylbutylammonium hydrogen sulfate,

DMBA][HSO ], under the optimised pretreatment conditions

of 30 min at 170°C.

TEA][HSO

4

] and

[

4

Figure 11 Saccharification yield (from air-dried pulps) and lignin and pulp

[

4

]

has been successfully applied for the recovery after pretreatment at 170°C for 30 min with three protic hydrogen

_f_r_a_c_t_i_o_n_a_t_i_o_n_o_f_M_i_s_c_a_n_t_h_u_s_,₁6,22 _s_u_g_a_r_c_a_n_e_b_a_g_a_s_s_e_,17 _w_i_l_l_o_w18

sulfate ILs, each containing 20 wt% water. Pine was pretreated at a solid to

solvent ratio of 1:10 g/g.

and switchgrass,¹⁴while the asymmetric [DMBA][HSO

never been used as a fractionation solvent. We were particularly

interested in applying [DMBA][HSO ] due to it being a liquid

4

] has

4

HSQC NMR spectroscopy of the lignins isolated from different

at room temperature, even in the absence of water, and hence it ionic liquids showed a decrease in the quantity of ether bonds

having a low viscosity, which facilitates handling in the lab and in the lignin in the order [TEA]>[HBim]>[DMBA], with

_a_t_s_c_a_l_e_.₅2 It has also been shown to be very effective in

_h_y_d_r_o_l_y_s_i_n_g_β_-_O_-₄_l_i_n_k_a_g_e_s_i_n_a_l_i_g_n_i_n_m_o_d_e_l_c_o_m_p_o_u_n_d_.₅3 We

volume integral sizes for the β-O-4’ bond of 13.6 vs 10.4 and

6.9%, respectively (Figure 12), which again is in line with the

have previously demonstrated that the optimum pretreatment

conditions for 1-butylimidazolium and triethylammonium

hydrogen sulfate solutions are the same, if the acid base ratio is

the same.¹⁶^,²³

The saccharification yields and lignin and pulp recoveries

obtained for 10 % solid loadings are shown in Figure 11. We

obtained the highest saccharification yields for [DMBA][HSO

4

]

(74%), showing that a lower-cost trialkylammonium hydrogen

sulfate IL can achieve similar or an even better pretreatment

This journal is © The Royal Society of Chemistry 2012

J. Name., 2012, 00, 1-3 | 8

View Article Online

DOI: 10.1039/C8GC02155D

Page 9 of 13

Journal Name

Green Chemistry

ARTICLE

decreasing rate constant observed for the three ILs. Table 2 Molar mass and polydispersity of lignins recovered after pretreatment of pine

wood at 170°C for 30 min with three low-cost hydrogen sulfate ILs. A solid to solvent

ratio of 1:10 g/g was used.

IL

M

n

M

w

PDI

3.7

3.9

5.1

[TEA][HSO

[HBim][HSO

[DMBA][HSO

4

]

922

967

775

3452

3810

3949

4

]

4

]

w n

M : Average molar masss, M : number average molar mass, PDI:

Polydispersity index

Experimental

Materials

Starting materials for ionic liquid synthesis were purchased

from Sigma Aldrich and used as received, unless stated

otherwise. H NMR spectra were recorded on a Bruker 400

The degree of condensation in the lignin, evidenced by a more

intense G2,cond signal, increased in the same order. The lignin

isolated using [DMBA][HSO ] can therefore be regarded as the

4

most modified lignin. Together with the high lignin precipitate

yield obtained with this IL, these data suggest that lignin

extraction was faster, probably due to a combination of

improved mass transfer due to the low viscosity of

1

MHz spectrometer. Chemical shifts (δ) are reported in ppm, the

1

13

DMSO signal at 2.500 ( H dimension) and 39.520 ( C

dimension). Electrospray mass spectrometry experiments were

carried out by Dr Lisa Haigh (Imperial College London,

Chemistry Department) on a Micromass Premier spectrometer.

The Karl-Fisher titrator used in this work was a V20 volumetric

Titrator (Mettler-Toledo) and the analytical balance a Sartorius

CPA 1003 S balance (±0.001 g).

[

DMBA][HSO

the acidic ionoSolv solution) and the higher reactivity of lignin

in [DMBA][HSO ]. A similar trend was observed for the

4

] (giving rise to longer lignin residence times in

4

average molar masses for the isolated lignins, as determined by

gel permeation chromatography (Table 2). Pretreatment with

Synthesis of 1-hydrogen-3-butylimidazolium hydrogen sulfate

[

DMBA][HSO

than applying the other two ILs. As a result, a high PDI of 5.1

was found for this IL vs. PDIs of 3.7 and 3.9 for [TEA][HSO

and [HBim][HSO ], respectively. We note that the lignin

obtained under optimised conditions with [DMBA][HSO ] has

a notably higher PDI than those observed with the other two

ILs, or for Miscanthus pretreated with [TEA][HSO ] at

_o_p_t_i_m_i_s_e_d_c_o_n_d_i_t_i_o_n_s_,₂2 however, willow pretreatment with

TEA][HSO ] has resulted in similarly high PDIs of 4.6 up to

4 n w

] yielded a lower M and a higher M lignin

[

HBim][HSO

M H SO (322 mL, 1.61 mol) was cooled with an ice bath.

Under stirring, 200 g of freshly distilled N-butylimidazole

1.61 mol) was added dropwise. The water was removed under

4

].

5

2

4

]

4

(

4

reduced pressure and the product dried in vacuum at 50°C

overnight. The ionic liquid was recovered as a clear, pinkish,

4

1

viscous liquid. H NMR: δH (400 MHz, DMSO-d

6

)/ppm: 9.14

(

s, 1H, N-CH-N), 7.79 (s, 1H, N-CH), 7.68 (s, 1H, N-CH), 4.26

(br, N-H, HSO ), 1.77 (m, 2H,

^-), 4.19 (t, J = 7.2 Hz, 2H, N-CH

N-CH -CH ), 1.23 (m, 2H, N-CH -CH -CH ), 0.88 (t, J = 7.4

Hz, 3H, N-CH -CH -CH -CH

). ¹³C NMR: δC (101 MHz,

DMSO-d )/ppm: 135.72 (N-CH-N), 122.46 (N-CH), 120.45 (N-

CH), 48.68 (N-CH

CH ), 13.75 (N-CH

[

4

_o_v_e_r₆_f_o_r_o_p_t_i_m_i_s_e_d_s_u_g_a_r_r_e_l_e_a_s_e_.₁8

4

2

3

6

2

), 31.90 (N-CH

-CH -CH -CH

3

2

-CH

).

2

), 19.29 (N-CH

2

-CH

2

-

2

+

-

MS (Magnet FB ) m/z: 125 ([HBim] , 100%), (Magnet FB )

m/z: 79 ([HSO

4

]^-, 100%).

Synthesis of triethylammonium hydrogen sulfate [TEA][HSO4].

Triethylamine (75.9 g, 750 mmol) was cooled with an ice bath

in a round-bottom flask. 150 mL 5 M H SO (750 mmol) was

2 4

added dropwise while stirring. The water was removed using a

rotary evaporator and the product dried using the Schlenk line

at 40°C overnight. The ionic liquid was recovered as a white,

Figure 12 Abundance of ether linkages and C-H motives on the guaiacyl ring in hygroscopic solid.

pine lignin recovered after pretreatment at 170°C for 30 min with three protic

hydrogen sulfate ILs containing 20 wt% water, according to HSQC NMR

spectroscopy. Pine wood was pretreated at a solid to solvent ratio of 1:10 g/g.

1

-_,

4

H NMR: δH (400 MHz, DMSO-d

6

)/ppm: 3.39 (s (br), HSO

N-H ), 3.10 (q, J = 7.3 Hz, 6H, N-CH ), 1.20 (t, J=7.3 Hz, 9H,

N-CH -CH

). ¹³C NMR: δC (101 MHz, DMSO-d

N-CH ), 9.15 (N-CH -CH ).

+

2

3

6

)/ppm: 46.21

(

2

3

+

-

MS (Magnet FB ) m/z: 102 ([TEA] , 100%), (Magnet FB )

m/z: 79 ([HSO

4

]^-, 100%).

J. Name., 2012, 00, 1-3 | 9

View Article Online

DOI: 10.1039/C8GC02155D

Green Chemistry

Page 10 of 13

Journal Name

ARTICLE

Synthesis of N,N-dimethylbutylammonium hydrogen sulfate

Saccharification assays were carried out according to a protocol

published by the NREL⁵⁵in triplicates with blanks (also

triplicates). All reagents were purchased from Sigma Aldrich.

The detailed procedure can be found in the ESI.

Hydrolysis was run for 7 days and Novozymes experimental

enzyme mixture NS-22201 was used as the enzymes. Analysis

was performed on a Shimadzu HPLC system with RI detector

and an Aminex HPX-87P column (BioRad, 300 x 7.8 mm) with

purified water as mobile phase (0.6 mL/min).

[

DMBA][HSO

N,N-dimethylbutylamine (75.9 g, 750 mmol) was cooled with

an ice bath in a round-bottom flask. 150 mL of 5 M H SO

750 mmol) was added dropwise while stirring. The water was

4

].

2

4

(

removed using the rotary evaporator and the product dried

using the Schlenk line at 70°C overnight. The ionic liquid was

recovered as a clear, viscous liquid.

1_H_N_M_R_:_δ_H₍₄₀₀_M_H_z_,_D_M_S_O_-_d

6

)/ppm: 9.24 (s, 1H, N-H),

), 2.76 (d, J = 4.3 Hz, 6H,

), 1.64 – 1.51 (m, 2H, N-CH -CH ), 1.29 (h, J = 7.4

Hz, 2H, N-CH -CH -CH ), 0.89 (t, J = 7.4 Hz, 3H, N-CH

CH -CH -CH )/ppm:

). ¹³C NMR δC (101 MHz, DMSO-d

6.62 (N-CH

CH -CH -CH

3

.02 (dt, J = 12.9, 5.0 Hz, 2H, N-CH

2

Lignin characterisation

N-(CH

)

3 2

2

-

HSQC NMR spectroscopy

2

3

6

Circa 20 mg of isolated lignin was dissolved in 0.25 mL of

DMSO-d and the solution transferred to a Shigemi tube.

6

HSQC NMR spectra were recorded on a Bruker 600 MHz

spectrometer (pulse sequence hsqcetgpsi2, spectral width of 10

5

2

), 42.48 (N-CH

), 13.71 (N-CH

3

), 25.82 (N-CH

2

-CH

).

2

), 19.40 (N-

2

-CH -CH -CH

2

+

3

+

-

MS (Magnet FB ) m/z: 102 ([DMBA] , 100%), (Magnet FB )

m/z: 79 ([HSO

4

]^-, 100%).

1

13

ppm in F2 ( H) with 2048 data points and 160 ppm in F1 ( C)

with 256 data points, 16 scans and 1 s interscan delay). Spectra

were analysed using MestReNova (Version 8.0.0, Mestrelab

Research 2012). All spectra were referenced to the DMSO peak

Feedstock

Pinus sylvestris was obtained from Metla (Finnish Forest

Research Institute). It was air-dried, ground and sieved (180-

1

13

at 2.500 ppm ( H) and 39.520 ppm ( C). Integrals were

obtained for spectra of the same series of experiments

simultaneously to ensure that the same areas were integrated.

All relevant spectra were copied into one file and selected them

while integrating the relevant area in one spectrum. Integration

areas were selected visually according to peak assignments

8

50 µm, 20 + 80 US mesh scale) prior to use and stored in

plastic bags at room temperature in the dark.

Fractionation of Biomass

Pretreatments, determinations of oven dried weight and ionic

liquid water content measurements were conducted according

found in literature.²¹For ether linkages, the C-H

integrated. Integral sizes are reported with respect to 100

+G2,cond) signals. All spectra can be found in the ESI.

α

-signals were

1

5

to the standard operating procedures from our laboratory , in

triplicate. A biomass to solvent ratio of 1:20 to 1:2 g/g was used

(G

2

(ODW basis). Hydrogen sulfate ionic liquids with 20wt% water

were used as the solvent, using between 2 and 10 g of ionic Gel permeation chromatography

liquid-water mixture and 1 g of biomass, except for the 1:20 g/g

GPC measurements were performed using an Agilent 1260

Infinity instrument equipped with a Viscotek column set

AGuard, A6000M and A3000M). The Agilent 1260 Infinity

RID detector was used for detection. GPC grade DMSO

containing LiBr (1 g/L) was used as eluent at a flow rate of 0.4

mL/min at 60°C. Samples were prepared by dissolving 20 mg

lignin in 1 ml eluent and filtering through a 0.2 µm syringe

filter. Ten pullulan standards (Agilent calibration kit, 180 < Mp

experiment, where only 0.5 g of biomass and 10 g of IL-water

mixture was used. A detailed description of the procedure can

be found in the ESI.

(

For experiments without air-drying of the pulp, the procedure

was followed unchanged until completion of the Soxhlet

extraction step. After the extraction, the pulp containing

thimbles were transferred from the Soxhlet adapter into 50 mL

centrifuge tubes and DI water was added immediately. This was

incubated for at least an hour. The thimble was removed from

the plastic tube and the pulp transferred back to the centrifuge

tube using a spatula. The suspensions were centrifuged for 30

<

780,000) were used to calibrate the instrument.

Conclusions

min at 2000G and the supernatant decanted. The wet pulps We have demonstrated the successful application of easily-

were weighed and their moisture content determined synthesised protic ionic liquids for the pretreatment of the

immediately. Thereafter, the pulps were stored in the fridge at recalcitrant softwood, pine. A highly digestible cellulose pulp is

4

°C.

obtained, giving rise to quantitative glucose yields after only

0 min of pretreatment at 170°C. Quantitative glucose release

was achieved at a solid to liquid ratio of 1:10 g/g using 1-

3

Compositional Analysis

Compositional analysis was carried out according to a butylimidazolium hydrogen sulfate, when the pulp drying step

published procedure by the National Renewable Energy was omitted. High saccharification yields were correlated with

_L_a_b_o_r_a_t_o_r_y₍_N_R_E_L₎_.₅4 The detailed procedure can be found in

extensive lignin removal from the pine wood.

the ESI.

Carbohydrate free lignins were isolated through antisolvent

(

water) addition and were found to be depolymerised and

Saccharification Assay.

partially condensed.

J. Name., 2012, 00, 1-3 | 10

View Article Online

DOI: 10.1039/C8GC02155D

Page 11 of 13

Journal Name

Green Chemistry

ARTICLE

Furthermore, we show that high solids loading of up to 1:2 g/g

achieve good pine fractionation, especially if the cellulose-rich

pulp is not air-dried. It may be possible to devise an adapted 11

Stavila, J. Pelton, H. Blanch, B. a. Simmons and A. George, Green

Chem., 2014, 16, 1236–1247.

S. H. Lee, T. V Doherty, R. J. Linhardt and J. S. Dordick,

Biotechnol. Bioeng., 2009, 102, 1368–76.

washing protocol that reduces re-precipitation and/or removes

1

2

3

4

X.-F. Tian, Z. Fang, D. Jiang and X.-Y. Sun, Biotechnol. Biofuels,

re-precipitated lignin from the pulp surface, further improving

the performance of ionoSolv pretreatment of softwood at high

solids loadings.

2

011, 4, 1–14.

M. T. Clough, K. Geyer, P. a Hunt, J. Mertes and T. Welton, Phys.

Chem. Chem. Phys., 2013, 15, 20480–95.

4

The ultra low-cost ionic liquid [DMBA][HSO ] proved to be a

A. George, A. Brandt, K. Tran, S. M. S. N. S. Zahari, D. Klein-

Marcuschamer, N. Sun, N. Sathitsuksanoh, J. Shi, V. Stavila, R.

Parthasarathi, S. Singh, B. M. Holmes, T. Welton, B. A. Simmons

and J. P. Hallett, Green Chem., 2015, 17, 1728–1734.

more effective pretreatment solvent than [HBim][HSO

the conditions studied.

4

] under

The potential to use low-cost ionic liquids as effective

pretreatment media for softwoods is very encouraging, as

ionoSolv pretreatment has the potential not only to be

economically viable but also to be feedstock independent,

which is a unique combination.

1

5

6

F. J. V. Gschwend, A. Brandt, C. L. Chambon, W.-C. Tu, L.

Weigand and J. P. Hallett, J. Vis. Exp., 2016, e54246.

A. Brandt-Talbot, F. J. V. Gschwend, P. S. Fennell, T. M.

Lammens, B. Tan, J. Weale and J. P. Hallett, Green Chem., 2017,

1

9, 3078–3102.

Acknowledgements.

17

C. L. Chambon, T. Y. Mkhize, P. Reddy, A. Brandt-Talbot, N.

Deenadayalu, P. S. Fennell and J. P. Hallett, Biotechnol. Biofuels,

The authors wish to acknowledge financial support from the

Grantham Institute for Climate Change and the Environment

and Climate-KIC for a studentship for FJVG, and the

Engineering and Physical Sciences Research Council (EPSRC;

EP/K014676/1 and EP/K038648/1) for funding for ABT.

CLC is grateful for funding in the form of an Imperial College

President’s Scholarship (EPSRC).

2

018, 11, 247.

1

2

8

9

0

1

2

3

4

L. Weigand, S. Mostame, A. Brandt-Talbot, T. Welton and J. P.

Hallett, Faraday Discuss., 2017, 202, 331–349.

A. Brandt, J. Gräsvik, J. P. Hallett and T. Welton, Green Chem.,

2

013, 15, 550–583.

X. Pan, D. Xie, R. W. Yu and J. N. Saddler, Biotechnol. Bioeng.,

2

008, 101, 39–48.

A. Brandt, L. Chen, B. E. van Dongen, T. Welton and J. P. Hallett,

Green Chem., 2015, 17, 5019–5034.

Notes and references

Department of Chemical Engineering, Imperial College London, London,

UK, SW7 2AZ. Tel: 44 2075945388 E-mail: j.hallett@imperial.ac.uk

F. J. V. Gschwend, F. Malaret, S. Shinde, A. Brandt-Talbot and J.

P. Hallett, Green Chem., 2018, 20, 3486–3498.

†

Electronic Supplementary Information (ESI) available: [details of any

P. Verdía, A. Brandt, J. P. Hallett, M. J. Ray and T. Welton, Green

Chem., 2014, 16, 1617–1627.

supplementary information available should be included here]. See

DOI: 10.1039/c000000x/

L. Chen, M. Sharifzadeh, N. Mac Dowell, T. Welton, N. Shah and

1

2

3

World Economic Forum and Ellen MacArthur Foundation, The

New Plastics Economy - Catalysing Action, 2017.

J. P. Hallett, Green Chem., 2014, 16, 3098–3106.

2

5

6

Y.-H. P. Zhang, J. Ind. Microbiol. Biotechnol., 2008, 35, 367–75.

R. E. H. Sims, W. Mabee, J. N. Saddler and M. Taylor, Bioresour.

Technol., 2010, 101, 1570–1580.

D. Di Maio and D. Turley, Lignocellulosic feedstock in the UK,

York, 2014 (https://lb-net.net/wp-content/uploads/2015/04/LBNet-

Lignocellulosic-feedstock-in-the-UK.pdf).

A. J. Ragauskas, C. K. Williams, B. H. Davison, G. Britovsek, J.

Cairney, C. A. Eckert, W. J. Frederick, J. P. Hallett, D. J. Leak, C.

L. Liotta, J. R. Mielenz, R. Murphy, R. Templer and T.

Tschaplinski, Science, 2006, 311, 484–9.

2

7

T. E. Timell, Wood Sci. Technol., 1967, 1, 45–70.

28

L. Kumar, V. Arantes, R. Chandra and J. Saddler, Bioresour.

Technol., 2012, 103, 201–208.

4

5

P. Havlík, U. a. Schneider, E. Schmid, H. Böttcher, S. Fritz, R.

Skalský, K. Aoki, S. De Cara, G. Kindermann, F. Kraxner, S.

Leduc, I. McCallum, A. Mosnier, T. Sauer and M. Obersteiner,

Energy Policy, 2011, 39, 5690–5702.

29

K. A. Y. Koivu, H. Sadeghifar, P. A. Nousiainen, D. S.

Argyropoulos and J. Sipila, ACS Sustain. Chem. Eng., 2016, 4,

5238–5247.

L. Tao, A. Aden, R. T. Elander, V. R. Pallapolu, Y. Y. Lee, R. J.

Garlock, V. Balan, B. E. Dale, Y. Kim, N. S. Mosier, M. R.

Ladisch, M. Falls, M. T. Holtzapple, R. Sierra, J. Shi, M. a. Ebrik,

T. Redmond, B. Yang, C. E. Wyman, B. Hames, S. Thomas and R.

E. Warner, Bioresour. Technol., 2011, 102, 11105–11114.

30

C. Lai, M. Tu, Z. Shi, K. Zheng, L. G. Olmos and S. Yu,

Bioresour. Technol., 2014, 163, 320–327.

3

1

2

3

4

5

S. Jin, G. Zhang, P. Zhang, S. Fan and F. Li, Bioresour. Technol.,

2

015, 181, 270–274.

M. Normark, S. Winestrand, T. a Lestander and L. J. Jönsson, BMC

Biotechnol., 2014, 14, 1–12.

6

C. Sievers, M. B. Valenzuela-Olarte, T. Marzialetti, I. Musin, P. K.

Agrawal and C. W. Jones, Ind. Eng. Chem. Res., 2009, 48, 1277–

1

286.

P. Sannigrahi, S. J. Miller and A. J. Ragauskas, Carbohydr. Res.,

2

010, 345, 965–970.

7

8

9

1

J. B. Binder and R. T. Raines, Proc. Natl. Acad. Sci. U. S. A., 2010,

1

07, 4516–21.

C. Alvarez-Vasco and X. Zhang, Biomass and Bioenergy, 2017, 96,

9

6–102.

A. Brandt, M. J. Ray, T. Q. To, D. J. Leak, R. J. Murphy and T.

Welton, Green Chem., 2011, 13, 2489–2499.

L. T. P. Trinh, Y. J. Lee, J.-W. Lee and H.-J. Lee, Biomass and

Bioenergy, 2015, 81, 1–8.

D. Diedericks, E. van Rensburg, M. D. P. García-Aparicio and J. F.

Görgens, Biotechnol. Prog., 2011, 28, 76–84.

3

6

7

B. J. Cox and J. G. Ekerdt, Bioresour. Technol., 2013, 134, 59–65.

L. Matías and A. S. Jump, J. Exp. Bot., 2014, 65, 299–310.

0

N. Sathitsuksanoh, K. M. Holtman, D. J. Yelle, T. Morgan, V.

J. Name., 2012, 00, 1-3 | 11

View Article Online

DOI: 10.1039/C8GC02155D

Green Chemistry

Page 12 of 13

Journal Name

ARTICLE

3

8

X. L. Luo, J. Y. Zhu, R. Gleisner and H. Y. Zhan, Cellulose, 2011,

8, 1055–1062.

1

3

4

9

0

F. Hu and A. Ragauskas, RSC Adv., 2014, 4, 4317–4323.

H. Li, Y. Pu, R. Kumar, A. J. Ragauskas and C. E. Wyman,

Biotechnol. Bioeng., 2014, 111, 485–492.

4

1

2

3

4

5

W. Li, N. Sun, B. Stoner, X. Jiang, X. Lu and R. D. Rogers, Green

Chem., 2011, 13, 2038–2047.

K. Shimada, S. Hosoya and T. Ikeda, J. Wood Chem. Technol.,

1

997, 17, 57–72.

P. Mäki-Arvela, T. Salmi, B. Holmbom, S. Willför and D. Y.

Murzin, Chem. Rev., 2011, 111, 5638–5666.

R. Pettersen, The Chemistry of Solid Wood, American Chemical

Society, Washington, DC, 1984, vol. 207.

M. Sette, R. Wechselberger and C. Crestini, Chem. - A Eur. J.,

2

011, 17, 9529–9535.

4

6

7

H. Kim and J. Ralph, Org. Biomol. Chem., 2010, 8, 576–91.

B. Yang and C. E. Wyman, Biofuels, Bioprod. Biorefining, 2008, 2,

2

6–40.

4

8

A. Aden, M. Ruth, K. Ibsen, J. Jechura, K. Neeves, J. Sheehan, B.

Wallace, L. Montague, A. Slayton and J. Lukas, Lignocellulosic

Biomass to Ethanol Process Design and Economics Utilizing Co-

Current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for

Corn Stover, Golden, CO, 2002.

4

5

9

0

P. Oleskowicz-Popiel, D. Klein-Marcuschamer, B. a. Simmons and

H. W. Blanch, Bioresour. Technol., 2014, 158, 294–299.

T. Rashid, C. F. Kait, I. Regupathi and T. Murugesan, Ind. Crops

Prod., 2016, 84, 284–293.

5

1

2

Y. Ni and Q. Hu, J. Appl. Polym. Sci., 1995, 57, 1441–1446.

J.-P. Belieres and C. A. Angell, J. Phys. Chem. B, 2007, 111,

4

926–4937.

5

3

4

G. F. De Gregorio, C. C. Weber, J. Gräsvik, T. Welton, A. Brandt

and J. P. Hallett, Green Chem., 2016, 18, 5456–5465.

A. Sluiter, B. Hames, R. Ruiz, C. Scarlata, J. Sluiter, D. Templeton

and D. Crocker, Determination of Structural Carbohydrates and

Lignin in Biomass, Golden, CO, 2012.

5

M. G. Resch, J. O. Baker and S. R. Decker, Low Solids Enzymatic

Saccharification of Lignocellulosic Biomass, Golden, CO, 2015.

J. Name., 2012, 00, 1-3 | 12

Article Doi

Quantitative glucose release from softwood after pretreatment with low-cost ionic liquids

DOI: 10.1039/c8gc02155d

Source and publish data:

Authors:

Article abstract of DOI:10.1039/c8gc02155d

Full text of DOI:10.1039/c8gc02155d

Products guided by the article

R&D Labs maybe for 2399-73-7

Relevant to this article

Hot Product