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TRANSCRIPT
Abstract— This study aims to investigate a novel pretreatment
method of sugarcane bagasse (SCB) as an essential step for
production of second generation bioethanol. Effect of tween 80 (TW)
and polyethylene glycol 4000 (PEG) on SCB pretreatment using 1-
butyl-3-methyl imidazolium chloride ([BMIM]Cl) as an ionic liquid
(IL) was assessed. Various concentrations of TW and PEG were
utilized to determine the optimum concentration of surfactant
resulting in high cellulose conversion. Both of surfactants increased
the sugar yield of enzymatic saccharification compared to IL only
pretreated SCB and untreated SCB but, PEG in 3% w/w exhibited
significantly enhanced enzymatic digestibility with an efficiency of
96.2% after 12 h of hydrolysis, which was 23% higher than the
efficiency observed for the IL pretreated SCB.
Keywords—1-butyl-3-methyl imidazolium chloride,
Pretreatment, Sugarcane bagasse, Surfactant
I. INTRODUCTION
IGNOCELLULOSIC biomass has potential to serve as a
low cost and renewable feedstock for bioconversion into
fermentable sugars, which can be further utilized for biofuel
production [1]. Pretreatment of lignocellulosic biomass prior
to use as feedstock for biofuel and chemical production is
required either to disrupt the crystalline structure of cellulose,
remove hemicellulose, remove or modify the lignin to increase
the exposure of cellulosic substrate to hydrolytic enzymes,
decrease cellulosic substrate recalcitrance for enzyme attack
and thus increase glucose yield [2]. The very complex
structure of lignocellulosic biomass makes it highly resistant to
enzymatic hydrolysis which results in low sugar yields [3].
Pretreatment is the most challenging step in bioethanol
production from lignocelluloses. Pretreatment disrupts the
compact and highly ordered structure of lignocelluloses so
enhances the sugar yield of enzymatic hydrolysis of biomass.
While all of the pretreatment methods result in enhanced
enzymatic saccharification of the residual polysaccharide, an
effective process that is inexpensive with low capital costs and
minimal impact on downstream processing has yet to be
developed. More recently, ionic liquids (IL) has emerged as a
promising method for lignocellulosic pretreatment as they
Niloofar Nasirpour is with the Tarbiat Modares University, Tehran, Iran
(e-mail: [email protected]).
Seyyed Mohammad Mousavi is with the Tarbiat Modares University,
Tehran, Iran (corresponding author: Tel.: +98-21-82884917; fax: +98-21-
82884931 ; e-mail: [email protected]).
exhibit outstanding physical and chemical properties [4].
Several reports were available on the pretreatment of
lignocellulosic biomass using various ILs [1]-[5], but
combination of surfactants and IL as a pretreatment agent has
not been studied yet. Lignin is widely recognized to be an
obstacle to efficient enzymatic hydrolysis. First, it
unproductively adsorbs a large fraction of the cellulase,
making it unavailable for enzymatic hydrolysis of cellulose
[6]. On top of that, lignin impedes enzyme access to cellulose
and hemicellulose, resulting in extended reaction times to
achieve high conversions. Thus, it would be beneficial to use
synergistic effect of IL and surfactant for delignification of
biomass.
In the present study, the surfactant-assisted ionic liquid
pretreatment of sugarcane bagasse was investigated for
enhanced enzymatic hydrolysis. Tween 80 and polyethylene
glycol 4000 were as additive surfactants, and [BMIM]Cl was
applied as the solvating ionic liquid. Experiments carried out
at 130 °C for 90 minute.
II. MATERIALS AND METHODS
A. Feedstock and materials
Sugarcane bagasse was supplied by the Iranian Research
Organization for Science and Technology (IROST). Samples
were ground in a cutter mill (Moulinex, AR1044) and passed
through sieves of mesh size 30 and 70. Ionic liquid [BMIM]Cl
was purchased from Sigma-Aldrich. Commercial enzymes of
Celluclast 1.5 L (the cellulases from Trichoderma ressei) and
Novozyme 188 (the cellubiase from Aspergillus niger) were
purchased from Sigma- Aldrich.
B. Surfactant assisted ionic liquid pretreatment
The amount of solid biomass subjected to pretreatment was
0.5 g of pre-milled SCB based on dry weight. All samples
were soaked into the surfactant of determined concentration
over-night to assure sufficient penetration of liquid into the
SCB solids. Subsequently, ionic liquid was added to sample
tubes so that the ratio of IL to solid content was 10:1. The
mixture was heated in an oil bath of 130 ºC for 90 min.
Following pretreatment, 5 ml deionized water was added into
the reaction mixture. The solution was mixed and centrifuged
(Vifion, VF550) at 12000 rpm for 10 min. To remove the
residual IL from the regenerated cellulose, biomass was
washed with 10 ml deionized water for three times. Wet
regenerated SCB was then freeze dried for 24 hours, prior to
Impact of Surfactant on the Ionic Liquid
Pretreatment of Sugarcane Bagasse
Niloofar Nasirpour, and Seyyed Mohammad Mousavi
L
3rd International Conference on Chemical, Ecology and Environmental Sciences (ICEES'2014) March 19-20, 2014 Abu Dhabi (UAE)
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enzymatic hydrolysis, and further analysis.
C. Enzymatic hydrolysis
Enzymatic saccharification was carried out with 2.5% w/v
of pretreated and untreated SCB in 10 mM of citrate buffer in
pH 4.8. Sodium azide was utilized in 0.02% to prevent
bacterial growth. The substrates were hydrolyzed with
Celluclast 1.5 L at 50 FPU /g substrate and Novozyme 188 at
40 CBU/g substrate. Samples were taken at 0, 3, 6, 12, 24, 48
and 72 h. Collected samples were centrifuged (B. Braun A15)
at 13500 rpm. Concentration of reduced sugars was measured
by utilizing DNS (3,5- dinitrosalicylic acid) method [13]. All
experiments were performed in duplicate.
III. RESULTS AND DISCUSSION
TW and PEG were added to SCB at concentration of 1, 3
and 5% w/w before IL pretreatment. Fig. 1 shows the kinetic
of enzymatic hydrolysis reaction of untreated and pretreated
SCB by IL and different TW concentrations. It is observed that
addition of tween 80 have increased the saccharification
efficiency compared to untreated and IL treated SCB, but
addition of 1% TW have minor effect compared to IL
pretreated SCB. TW with 5% concentration results in highest
sugar yield. Enzymatic digestibility of TW assisted IL
pretreatment of 1, 3 and 5% concentration after 24 h were
87.7, 93.6 and 99.7, respectively.
Fig 1 Kinetic of enzymatic hydrolysis reaction of untreated and
pretreated SCB by IL and different TW concentrations
Fig. 2 shows the kinetic of enzymatic hydrolysis of
untreated and pretreated SCB by IL and different PEG
concentrations. It is obvious that addition of PEG has
increased the efficiency of saccharification process, but similar
to the effect of TW, PEG concentration of 1% doesn’t have
substantial effect on the sugar release compared to the IL
pretreatment.
The optimum concentration of PEG was 3%, with an
efficiency of 96.2% after 12 h of hydrolysis, while increasing
the concentration to 5% the enzymatic digestibility decreased.
High concentration of PEG might occupy the hydrogen
bonding capacity of ionic liquid and thus the IL pretreatment
influence have decreased. However, this is not true for 5%
concentration of TW, as the hydrogen bonding capacity of TW
is different from PEG, because each has different chemical
bonds, interacting with lignocelluloses.
Fig. 2 Kinetic of enzymatic hydrolysis reaction of untreated and
pretreated SCB by IL and different TW concentrations
In the present study surfactants have influenced the substrate
structure and the performance of the surfactant is the structural
change of lignocelluloses as the lignin removal was increased
by surfactant addition. Following the pretreatment step the
SCB is completely washed, while it is possible that a little
amount of surfactant may remain in the pores of pretreated
SCB and affecting the enzymatic hydrolysis of substrate.
Irrespective of the mechanistic effect of surfactant on SCB
during the pretreatment or hydrolysis step, the ultimate result
is the higher concentrations of sugar.
IV. CONCLUSION
This study presents a novel and improved pretreatment
method for lignocelluloses. This research demonstrates the
effectiveness of surfactant addition before ionic liquid
pretreatment of a lignocellulosic biomass, sugarcane bagasse
(SCB). Enzymatic saccharification of surfactant-IL pretreated
samples increased 23% in comparison with IL pretreated
samples.
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