COST FP1105

Changes On Lignin Structure Influenced By The Ionic Liquid

Raquel Pradoa, Xabier Erdociab, Jalel Labidib, Tom Weltona

Department of chemistry, Imperial College London, London, UK a

Chemical and Environmental Engineering Department, University of the Basque Country, San Sebastian, Spain b

COST FP1105

Lignin

Lignin properties:

Polyphenol polymer

Aromatics source

50 million tons as residue per

year

Applications:

Adhesive

Bioactive

Binder

Antioxidant

% Softwood Hardwood Grasses

Coumaryl 5

Coniferyl 90-95 50 75

Sinapyl 5-10 50 25

B-O-4 46 60

A-O-4 6-8 6-8

4-O-5 3.5-4 6.5

B-5 9-12 6

B-1 7 7

B-B’ 2 3

5-5’ 9.5-11 4.5

COST FP1105

Ionic Liquids

Definition

They are salts in the liquid state

Their melting points are lower than 100 °C

Are composed by low symmetry cations and anions

Properties

Low melting point

Low vapour pressure

High thermal stability

High chemical stability

High ionic conductivity

Applications

Organic synthesis Solvent and catalyst

Separation processes

Electrochemistry

Tribology

Biorefinery

COST FP1105

Miscanthus characterization

Miscanthus composition

• Miscanthus is a rapid growth plant

% Standard Miscanthus

Moisture content TAPPI T264 cm-97 8.80±0.03

Ash TAPPI T211 om-93 4.2±0.5

Hot water solubility TAPPI T207 om-93 12.4±0.2

NaOH solubility TAPPI T212 om-98 36.8±0.7

Extractives TAPPI T204 cm-97 7.9±0.4

Lignin TAPPI T222 om-98 18.4±0.4

Hollocellulose 30±2

α-cellulose 36.2±0.2

COST FP1105

Experimental conditions

Synthesis of [HC4im][HSO4]

Drop-wise addition of H2SO4 on butyl imidazole

H2SO4 :butyl imidazole mass ratio 1:1

Magnetically stirred for 24 h and dried under vacuum

Synthesis of [Et3NH][HSO4]

Drop-wise addition of H2SO4 5 M on triethylamine

H2SO4 : triethylamine mass ratio 1:1

Magnetically stirred for 24 h and dried under vacuum

COST FP1105

Experimental conditions

Pretreatment

Miscanthus, water and IL ([Et3NH][HSO4] or

[HC4im][HSO4]) were homogeneously mixed in

a 1:2:8 mass ratio.

The mixtures were subjected to different

pretreatment times at 120 °C (8 h and 22 h).

Lignin precipitation

2 volumes of water were added to black liquor

It was centrifuged at 4000 rpm during 15 min

Washed with distilled water and dried at 70 ºC

during 16 h

IL + H2O + Miscanthus

Black liquor

Lignin

IL

Pulp

COST FP1105

Yields results

PretreatmentSample Solved

biomass (%)Lignin (%) S/GIL Time

[HC4im][HSO4]8 h Im 8 60 ± 1 14.64 ± 0.03 1.14

22 h Im 22 63.9 ± 0.5 30 ± 7 1.11

[Et3NH][HSO4]8 h Am 8 43.7±0.6 9.05 0.94

22 h Am 22 46.1±0.6 11.7±0.4 0.87

[HC4im][HSO4] was more active on biomass solubility and lignin extraction than [Et3NH][HSO4].

IL affect to S/G ratio:

[HC4im][HSO4] leads to higher amount of syringyl units.

[Et3NH][HSO4] leads to higher amount of guaiacyl and in both with the pretreatment time

syringyl units decreased.

COST FP1105

ATR-IR Characterization

[HC4im][HSO4]: at 2874 and 3143 cm-1 appeared

peaks assigned to stretching on imidazole ring due

to IL contamination.

[Et3NH][HSO4]: at 1268 and 1326 cm-1

appeared bands related with guaiacyl ring

stretching and deformation.

COST FP1105

Py-GCMS characterization

Butyl imidazole

Sugars Phenolics Fatty acids [HC4im][HSO4]: There was butyl

imidazole contamination and

higher proportion of sugar.

[Et3NH][HSO4]: Fatty acid

proportion was higher and there

was no IL contamination.

COST FP1105

HPSEC Characterization

Sample MW Mn PolydispersityIm 8 6,820 1108 5.65Im 22 14,726 2824 5.22Am 8 36,156 1760 20.99Am 22 10,142 1643 6.17

[HC4im][HSO4]: Mw increased

with the pretreatment time,

but polydispersity decreased.

[Et3NH][HSO4]: Mw and

polydispersity decreased with

the pretreatment time.

COST FP1105

Conclusion

[HC4im][HSO4] showed higher reactivity. But the obtained lignin was contaminated by

imidazole ring.

S/G ratio was also affected by the IL, as it was observed by ATR-IR and py-GCMS:

[HC4im][HSO4] lignin had higher amount of syringyl.

[Et3NH][HSO4] lignin had higher amount of guaiacyl.

Lignin structure was affected by the IL.

COST FP1105

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