The document compares dilute acid and ionic liquid pretreatments of switchgrass and finds that ionic liquid pretreatment more effectively removes lignin, disrupts the plant structure, reduces cellulose crystallinity, and results in higher enzyme hydrolysis rates compared to dilute acid pretreatment, however ionic liquid pretreatment is a newer method and has higher costs than dilute acid pretreatment.

1. Chenln Li, Bernhard Knierim, Chithra Manisseri, Rohit Arora, Henrik V. Scheller, Manfred
Auer, Kenneth P. Vogel, Blake A. Simmons, Seema Singh
Auer P Vogel A Simmons
Lis Nimani
Biological Systems Engineering
October 29th, 2010

2.  Pretreatment is a very important step in
Lignocellulosic biomass conversion.
Li ll l i bi i
◦ Accounts for 16-19% of total Capital Investment (Sousa et al.,
2009).
◦ E h
Enhances rate of hydrolysis 3-10 f ld
t f h d l i 3 10 fold.
◦ Separates Lignin and Hemicellulose for value added products.
 Objectives of Pretreatment:
◦ Remove cross-linked matrix of lignin and hemicellulose that
embeds cellulose.
◦ Disrupt crystalline structure of cellulose.
◦ D t
Destroy matrix structure of f d t k
t i t t f feedstock.
◦ Increase surface area.

3.  Several Pretreatment technologies are available:
 Dilute Acid
 Ionic Liquid
 Steam Explosion
 Ammonia Fiber Explosion
 Organoslov
 SPORL
 Hot Water
 Lime
 And more…

4. Dilute Sulfuric Acid Pretreatment
Vs.
Vs
Ionic Liquid Pretreatment

5.  Dilute Sulfuric Acid Pretreatment
◦ Leading pretreatment process under commercial development.
d d ld l
◦ Works well with herbage, hardwood, but not softwood.
• R
Reactions th t t k place t Li
ti that take l to Lignocellulose:
ll l
 Cellulose: Partial degradation of the cellulose (amorphous).
 Hemicellulose: Dissolved by acidic hydrolysis.
 Formation of inhibitory compounds to fermentation organisms.
 Lignin: Condensed Lignin remains on cellulose.

6.  Ionic Liquid Pretreatment
◦ Use of Ionic Liquid Solvents for Pretreatment Purposes.
f dS l f
 Separation of Lignocellulose.
 Cellulose recovered with anti-solvent solutions.
 Disruption of cellulose structure.
structure
◦ Ionic liquids are organic salts that are liquid at room temperature
and are stable to 300 °C.
◦ 1-ethyl-3-methylimidazolium acetate ([
y y ([C2mim][Oac]) can
][ ])
solubilize switchgrass and reject lignin from the recovered
polysaccharide.
 This Ionic liquid has been shown to increase the Cellulase activity on Cellulose.
◦ R
Recent R
t Reports h
t have also shown th complete di
l h the l t dissolution and
l ti d
partial delignification of sugarcane, softwood and hardwood in
various ionic liquids.

7. ◦ Biomass: Switchgrass (Panicum virgatum L.)
 Milled (Thomas Wiley Mill) with a 40 mesh screen Extraction with water followed
(Thomas-Wiley
with ethanol using NREL procedure.
◦ Enzymes: Cellulase, β-glucosidase
◦ Ionic Liquid: 1-ethyl-3-methylimidazolium acetate ([C2mim][Oac])
◦ Acids/Basses: Acetic Acid Sodium Acetate Sulfuric Acid
Acid, Acetate, Acid,
3,5-dinitrosalicylic Acid, Trifluoroacetic Acid, NaOH

8.  Ionic Liquid Pretreatment:
◦ 3% (w/w) switchgrass solution prepared.
 (300 mg of Switchgrass with 9.7 g [C2mim][OAc].
o Heated and stirred at 160 °C for 3 hr.
o After 3 hr incubation water added for regeneration of
hr. incubation,
dissolved cellulose, then centrifuged for 10 min.
 Cellulose I⇀Cellulose II (Stable Form)
 Dilute Acid Pretreatment:
◦ Switchgrass presoaked at room temperature with 1.2% (w/w)
sulfuric acid at 3% (w/w) total solid loading for 4 hr
hr.
◦ Samples were than heated at 160 °C for 20 min.

9. •Table 1 summarizes the various pretreatment conditions and the various amounts
of cell wall components.
•Both Dilute Acid and Ionic liquid pretreatments remove hemicellulose and lignin.
•Dilute Acid removed 22.4 % lignin.
•IL removed 69 2 % li i i )
IL d 69.2 lignin, ie)
•IL pretreatment removes more lignin and less hemicellulose than dilute acid
pretreatment.
•IL produces recovered materials with hi h sugar and l
IL d d i l i h higher d less li i
lignin.

10. •Figure above represents sugar yields and monosaccharide composition.
•This Analysis was done using HPAEC on dissolved material after pretreatment.
•Dilute Acid Removes the majority of hemicellulose as well as some cellulose.
•Hemicellulose removal is less in Ionic Liquid Pretreatment.
•From Table 1: There is 87 % and 81% loss in Hemicellulose between Dilute Acid and
Ionic liquid Pretreatments respectively.

11. •Table 2 data indicates the Crystallinity (CI) index as well the amount of sugar that
Table index,
was hydrolyzed. This data was taken using powder X-ray diffraction.
•Crystallinity affects the amount of hydrolysis of cellulose.
•Amorphous vs Crystalline
Amorphous vs.
•IL pretreatment makes cellulose amorphous changing it from cellulose I to Cellulose
II. Thus, greater potential for hydrolysis.
•Dilute Acid has higher CI. This is due to amorphous breakdown.
•It does not have the ability to breakdown the H-bonds between fibrils.

12. •Chemical Fingerprinting
•ATR-FTIR: (7 bands on Figure 2)
•Band at 1510 and 1329(1/cm)
•Indicates Lignin molecule.
•Are smaller for IL than DA, UN.
•Band at 1100 (1/cm)
•Indicates Crystalline Cellulose.
•Missing for IL; Increasing for DA.
•Band at 900 (1/cm)
•Indicates Amorphous Cellulose.
•Are smaller for DA than IL.
Indicating Increased CI for
Dilute Acid Pretreatment.
•Band at 1056, 1235, and 1375 (1/cm).
•Indicates Hemicellulose
Figure 2: ATR-FTIR, Raman Spectra •Significant Decrease for DA indicating
removal of Hemicellulose.

13. •Ratio of 1500/900 (1/cm)
•Indicates Lignin/Cellulose
•IL<DA as indicated in Table 3:
IL<DA i di t d i T bl 3
•Raman Spectra: (Figure 2)
•Provides Molecular Understanding
•Lignin features monitored.
•1600 (1/cm)-lignin aromatic ring
•1620 (1/cm)-Ring Conj. C=C bond.
Data Indicates that IL removes
much more lignin than DA.
Figure 2: ATR-FTIR, Raman Spectra

14. Figure 4: SEM Images of Untreated (a), Dilute Acid (b), Ionic Liquid (C)
g g
•Untreated: Highly fibrillar and intact morphology
•Dilute Acid: Cell wall not disrupted by pretreatment. Some lignin may
Dilute
be condensed on the surface of fibers.
•Ionic Liquid: Significantly alters fibrillar structure. No fibrous structure.

15. •IL pretreated showed higher kinetics
with digestibility reaching 96 % within
24 hrs.
•Initial rates of Ionic liquid were 16.7x
greater than Dilute Acid and 54 4
Dil te 54.4x
greater than untreated Switchgrass.
(Table 2).
•Reasons for higher Kinetics in IL:
Figure 5: Comparison of Saccharification by •Amorphous structure!
different pretreatments
•Less Lignin!

16.  Ionic Liquid Pretreatment offers advantages over Dilute Acid
Pretreatment:
1. Disrupts the matrix structure of switchgrass
2. Increases Surface Area
3. Reduces Crystallinity of Cellulose ⇒Amorphous
4.
4 Higher Delignification ⇒ Offers Purer Lignin for use of co-products.
co products
5. Higher enzyme hydrolysis
 Problems with Ionic Liquid Pretreatment
1. New Method
2. High Cost