4th International Conference on
Thermochemical Biomass Conversion Science
2-5th November, 2015
Bioeconomy Institute
Westin Chicago River North
Arpa Ghosh, Robert C. Brown, Xianglan Bai
Selective depolymerization of cellulose to solubilized carbohydrates in aprotic solvent systems
Product Distribution of Cellulose Solvolysis in Non-catalytic Aprotic Solvents at Supercritical State:
(Published, [1])
 Hot and pressurized polar aprotic solvents can rapidly decompose cellulose to produce significantly high
yields of solubilized carbohydrates (anhydrosugar levoglucosan is primary product). [1]
 This work continues to investigate the comparative study on the effect of polar aprotic solvents on the yields,
selectivity and stability of solubilized carbohydrates with and without the acid as catalyst.
Solubilized
carbohydrates of DP >1
Gamma valerolactone (GVL), and 1,4-Dioxane
Acetone
Ethyl acetate
15
1,4-dioxane
y = 0.9948x + 13.31
R² = 0.867
5
30
2 mM
20
10
0
70
60
50
40
30
20
10
0
0.1 mM
No acid
0
0
Solubilized product yield: 72-98%
Solubilized carbohydrate yield: 63-94%
Maximum LG yield: 15-38%
Acid catalyst: 0.1-5 mM sulfuric acid
Feedstock: Microcrystalline cellulose, Sigmacell, 50 m
Solvents: Acetone, Acetonitrile, Tetrahydrofuran (THF), Ethylacetate, Methyl iso-butyl ketone (MIBK),
20
AGF
High yield of solubilized carbohydrates using a wide
range of aprotic solvents.
Materials used:
THF
10
Levoglucosan (LG)
Experimental Method
MIBK
25
40
5
10
15
20
Polar solubility parameter, δP (MPa1/2)
Acetonitrile
THF
LG
Anhydro oligosaccharides
22
27
Retention time (min)
25
0
5
10
15
Time of reaction (min)
Temperature = 350oC, Initial cellulose = 20 mg
Aprotic Solvent
High polarity
Low polarity
High in
monomer
Low in
oligomers
Low in
monomer
High in
oligomers
Cellulose loading: 1-50 mg
Time of reaction: 0.75-16 min
20 mg cellulose reacted at
with and without
H2SO4 as catalyst
Heating bath: Techne Industrial
60
Fluidized Bed 51
Effectiveness factor =
0
Temperature = 350oC, Acid conc. = 0.25 mM
LG yield without acid catalyst
LG yield (%)
Fluidized
Bed Heater
No mixing
Cellulose feedstock
Gases
Solid residue
Polar aprotic solvent
40
With acid 0.5 mM
20
10
0
Solubilized
product
0.81
Ethyl acetate
1.46
Acetone
1.82
Dioxane
3.04
Acetonitrile
1.49
THF
1.86
GVL
1.33
Without acid
30
Reactor
Solvent system
Solvolysis Product Extraction and Analysis:
Physical Properties of the Solvents:
Polar Aprotic Solvent
Boiling point (oC)
Critical point
Polar Solubility
Parameters (MPa1/2)
1,4-Dioxane
101
314oC and 5.21 MPa
2.1
Ethyl acetate
77
260oC and 3.9 MPa
6.6
THF
66
268oC and 5.19 MPa
7.0
MIBK
116
298oC and 3.70 MPa
7.4
Acetone
56
235oC and 4.8 MPa
13.1
GVL
207-208
Not available
18.7
Acetonitrile
82
272oC and 4.87 MPa
22.1
Product Distribution in Acid-Catalyzed Cellulose Solvolysis in 1,4-dioxane:
Carbon yield (%)
 The product from solvent liquefaction of cellulose contains mainly solubilized products, solid residue
and negligible gases.
 The solubilized fraction was extracted out of the reactors, filtered and analyzed. The solid residue was
dried overnight at 50oC and weighed for mass.
 GC-MS(Agilent 7890B GC and 5977A MSD) was used for identification and GC-FID for quantification
of the products. HPLC and GFC were used for high molecular weight products.
50
45
40
35
30
25
20
15
10
5
0
LG
AGF
Solvolysis condition:
Temperature = 350 oC
Initial cellulose = 20 mg
Acid concentration = 0.25 mM H2SO4
5-HMF
Lgnone
Furfural
Acetic
acid
0
5
10
15
Time of reaction (min)
Additional products are solubilized carbohydrates with
DP > 1 (31% carbon yield)
Financial support from NSF EPSCoR and Iowa Energy Center is gratefully acknowledged.
Cellobiosan
Effectiveness factor
MIBK
 Enhanced yield of LG at a faster rate (43% in 2 min) in
presence of very dilute acid catalyst.
 Yield of secondary dehydration products suppressed at
minimal acid concentration.
 LG in the solvent phase is highly stable even at high
temperature.
 Solubilized carbohydrate yield improved from 63% to 74%
by adding acid to 1,4-dioxane.
300oC
40
30
20
250oC
0
2
4
Time of reaction (min)
Cello-oligosaccharides
50
350oC
0
5
10
Time of reaction (min)
Initial cellulose = 10 mg, Acid conc. = 0.25 mM
Multiple Products from One Solvent
System:
Cellulose
Solvent
50
375oC
10
LG yield with acid catalyst
70
10 mg
50 mg
Proposed Reaction Network for Acid-catalyzed
Cellulose Solvolysis in Aprotic Solvent:
350oC
60
20 mg
(Manuscript in preparation)
Batch reactor type: Stainless steel mini-reactor (SS-600-6BT) of 2.5 ml capacity
1 mg
 Highest yield of levoglucosan (43% LG yield) with least degradation was achieved at acid
concentration of 0.25 mM in 1,4-dioxane. Further increasing the acid-level resulted in increase of
secondary product yields.
 Lower mass loading helped in improving LG yields. Achieved up to 63% within only 5 min at 1 mg
cellulose loading.
 Increase of temperature also increases LG yield and shortens the reaction time (51% in 2 min).
Behavior of Aprotic Solvents in Acid-catalyzed Cellulose Solvolysis:
Reactor and Operating condition:
Effect of Temperature
LG yield (%)
5-HMF
30
0.25 mM
70
60
50
40
30
20
10
0
Levoglucosenone
(LGO)
Levoglucosan
(LG)
Maximum yield (%)
Solubilized Carbohydrates and
Minor Secondary Dehydration Products
Furfural
Acetonitrile
Effect of Mass loading of cellulose
LG yield (%)
Carbon yield (%)
Supercritical Polar Aprotic Solvent
50
GVL
35
Solid residue
100
90
80
70
60
50
40
30
20
10
0
Effect of Acid Concentration
40
LG yield (%)
Biomass/Cellulose
Effect of Reaction Conditions on LG Yields in 1,4-dioxane:
LG Yields Correlated with Solvent Polarity
Temperature 350oC and 20 mg Cellulose
Reaction time 8-16 min
Area (uRIU*min/g)
 Cellulose is the primary source of fermentable carbohydrates in biomass but it is inherently recalcitrant to
chemical and biological treatments.
 Conventional method of enzymatic hydrolysis suffers from slow conversion rates, limited by inhibitors,
involves costly enzyme production step.
Liquid hold-up: 1.2 ml
Temperature: 250-350oC
Results and Discussion
Results and Discussion
LG yield (%)
Introduction
Dehydration at 350oC using 20 mg cellulose
50
40
5-HMF
30
Furfural
20
LGO
10
0
5-HMF
Furfural
1,6-anhydro-betaD-glucofuranose
(AGF)
 Cellulose depolymerizes possibly through
formation of cello-oligosaccharides (cellobiosan)
to finally form monomeric products.
0.1 0.25 0.5
1
2
5
Acid concentration (mM)
 Changing the acid concentration can
increase the yield of useful dehydration
products such as levoglucosenone (LGO).
Conclusions
 A wide range of supercritical aprotic solvents could effectively depolymerize cellulose producing up
to 94% yield of solubilized carbohydrates within only 8-16 min without catalyst.
 Further enhancement of LG yield (15% to 43%) and other solubilized carbohydrate yield (63% to
74%) was possible at a shorter reaction time (2-7 min) by adding very dilute acid as catalyst.
 Effective solvent for maximizing the yield of LG could be identified based on its polar solubility
parameter and effectiveness factor in non-catalytic and acid-catalyzed condition, respectively.
 The selectivity and stability of LG in was high in 1,4-dioxane during the reaction.
 LG yield could be enhanced by optimization of reaction parameters (63% yield at very low mass
loading).
 Tuning operating conditions, it is possible to manufacture various useful chemical building blocks
including fermentable sugars using aprotic polar solvents.
References
[1] Ghosh, A., Brown, R. C., & Bai, X. Production of solubilized carbohydrate from cellulose using non-catalytic, supercritical
depolymerization in polar aprotic solvents. Green Chemistry 2015. DOI: 10.1039/C5GC02071A
[2] Bai, X. L.; Brown, R. C.; Fu, J.; Shanks, B. H.; Kieffer, M., The Influence of Alkali and Alkaline Earth Metals and the Role
of Acid Pretreatments in Production of Sugars from Switchgrass Based on Solvent Liquefaction. Energy & Fuels 2014, 28 (2),
1111-1120.