Synthesis and characterization of new low-cost ILs based on butylammonium cation and application to lignocellulose hydrolysis

Article abstract of DOI:10.1016/j.carbpol.2016.01.069

Fourteen ionic liquids (ILs) were obtained and characterized by nuclear magnetic resonance and infra-red spectroscopy. One of these liquids, n-butylammonium acetate, was used in the treatment of coir fiber prior to acid hydrolysis. For this purpose, the fiber was pulped with 8% (w/w) sodium hydroxide for 6 h under 2.5 atm pressure at 137 °C and then treated with IL for 2 h at 90 °C. The samples were hydrolyzed in acetic acid at different concentrations and temperatures. The reducing sugar concentrations were determined in all samples, and the optimal hydrolysis conditions were established (32.2% acetic acid at 122.4 °C). The reaction time was also studied, and the conversion was maximized at 3 h. Under the best hydrolysis conditions, crude fiber, pulping fiber, and IL-treated fiber were hydrolyzed to yield 8.53%, 47.58%, and 89.75% of reducing sugars, respectively.

Full text of DOI:10.1016/j.carbpol.2016.01.069

Accepted Manuscript
Title: Synthesis and characterization of new low-cost ILs
based on butylammonium cation and application to
lignocellulose hydrolysis
´
Author: Jose Carlos de Andrade Neto Allex de Souza Cabral
Lucas Rissato Dognani de Oliveira Ricardo Belchior Torres
´
Andreia de Araujo Morandim-Giannetti
PII:
S0144-8617(16)30033-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.carbpol.2016.01.069
CARP 10748
To appear in:
Received date:
Revised date:
Accepted date:
17-9-2015
29-1-2016
30-1-2016
Please cite this article as: Neto, J. C. A., Cabral, A. S., Oliveira, L. R. D., Torres,
R. B., and Morandim-Giannetti, A. A.,Synthesis and characterization of new low-
cost ILs based on butylammonium cation and application to lignocellulose hydrolysis,
Carbohydrate Polymers (2016), http://dx.doi.org/10.1016/j.carbpol.2016.01.069
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Synthesis and characterization of new low-cost ILs based on butylammonium cation and
application to lignocellulose hydrolysis
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José Carlos de Andrade Netoa, Allex de Souza Cabrala, Lucas Rissato Dognani de Oliveiraa,
Ricardo Belchior Torresa, Andreia de Araújo Morandim-Giannettia*
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aDepartamento de Engenharia Química, Centro Universitário da FEI, Av. Humberto de
Alencar Castelo Branco, 3972, 09850-901 São Bernardo do Campo - SP, Brazil
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author. Tel: +55-011-43532900. Fax: +55-01141095994.
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E-mail address: preamorandim@fei.edu.br (A. de A. Morandim-Giannetti)
Synthesis and characterization of new low-cost ILs based on butylammonium cation and
application to lignocellulose hydrolysis
Abstract
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Fourteen ionic liquids (ILs) were obtained and characterized by nuclear magnetic resonance
and infra-red spectroscopy. One of these liquids, n-butylammonium acetate, was used in the
treatment of coir fiber prior to acid hydrolysis. For this purpose, the fiber was pulped with 8%
(w/w) sodium hydroxide for 6 h under 2.5 atm pressure at 137 °C and then treated with IL for
2 h at 90 °C. The samples were hydrolyzed in acetic acid at different concentrations and
temperatures. The reducing sugar concentrations were determined in all samples, and the
optimal hydrolysis conditions were established (32.2% acetic acid at 122.4 °C). The reaction
time was also studied, and the conversion was maximized at 3 h. Under the best hydrolysis
conditions, crude fiber, pulping fiber, and IL-treated fiber were hydrolyzed to yield 8.53%,
47.58%, and 89.75% of reducing sugars, respectively.
Keywords: ionic liquid, lignocellulose hydrolysis, acid hydrolysis
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1. Introduction
The production of biofuels from lignocelluloses such as sugar cane, corn stover, wheat
straw, wood chips, rice straws, bamboo, napier grass, and coir is now attracting increasing
attention from researchers because these materials are available in large quantities and have
high carbohydrate contents (Guo, Su, Huang, Qi & He, 2015; Hu et al., 2013; Morandim-
Giannetti, Albuquerque, Carvalho, Silva Araújo & Magnabosco, 2013; Yu, Jameel, Chang,
Philips & Park, 2013; Xie et al., 2013).
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However, because all lignocellulosic materials are composed of cellulose (40–45%),
hemicellulose (30–35%), and lignin (25–30%), pretreatments are necessary (Gabhane, Prince
William, Vaidya, Das & Wate, 2015; Yin et al., 2014) to increase the availability of
fermentable sugars (Gunny, Arbain, Nashef & Jamal, 2015; ; Lin et al., 2015; Wang et al.,
2015; Bian et al., 2014; Xie et al., 2013; Shill, Miller, Clark & Blanch, 2012)).
Pretreatment is applied through various techniques such as acid or alkali treatments,
steam explosion, alkali-microwave, alkaline wet oxidation, autohydrolysis, ammonia
fiber/freeze explosion, pH-controlled liquid hot water, water–ethanol extraction (Organosolv
process), supercritical carbon dioxide, and organic solvents in ionic liquid (IL) hydrolysis
(Zhuo et al., 2015; Gunny et al., 2015; Xu et al., 2015; Bian et al., 2014; Morandim-Giannetti
et al., 2013; Hu et al., 2013; Shill et al., 2012).
These treatments interfere with the hydrogen bonds between the cellulose fibers. In
particular, they disrupt the π–π interactions between lignin and polysaccharides, thereby
decreasing the crystallinity and favoring hydrolysis (Nam, French, Condon & Concha, 2016;
Zhuo et al., 2015; Gunny et al., 2015; Xu et al., 2015).
Besides facilitating lignocellulose hydrolysis, these treatments accelerate the
conversion of biomass to fermentable sugars. By reducing the degree of crystallinity, they
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increase the surface area in contact with the hydrolyzing agent and remove lignin and
hemicellulose, which is necessary for bioethanol production (Nooria & Karimi, 2016;
Parveen, Patra & Upadhyayula, 2016; Serna, Alzate & Alzate, 2015; Gabhane et al., 2015;
Wang et al., 2015).
The agents used in current treatments, namely ILs or room temperature ILs (RTILs),
have been widely studied because of their special features. For instance, some salts exist in
the liquid state at room temperature. Moreover, these agents are lauded as green solvents in
various chemical processes (Lu et al., 2015; Berg, Harris, Riisager & Fehrmann, 2013; Hu et
al., 2013; Zhu, Cui, Zhang & Liu, 2011; Pham, Cho &Yun, 2010).
Two ILs, 1-ethyl-3-methyl-imidazolium acetate ([EMIM][OAc]) and 1-butyl-3-
methylimidazolium chloride ([BMIM][Cl]), have been shown to efficiently solubilize
cellulose and lignocellulose compounds in biomass treatment (Parveen et al., 2016; Bahrani,
Raeissi & Sarshar, M., 2015; Isik, Sardon & Mecerreyes, 2014; Lee et al., 2014; Lee, Viell et
al., 2013).
Other unique and important properties of ILs are their negligible vapor pressure, high
thermal stability, tunable viscosity, miscibility with water and organic solvents,
nonflammability, ability to dissolve many different organic, inorganic and organometallic
materials, and high thermal conductivity. They also serve as nonaqueous polar alternatives in
phase transfer processes (Keskin et al., 2007). These characteristics facilitate IL application in
different industrial areas such as extraction, separation, compound purification, and
dissolution of lignocelluloses (Gunny et al., 2015; Zhuo et al., 2015; Bian et al., 2014;
Naushad, AlOthman, Khan & Ali, 2012; Keskin et al., 2007). Moreover, IL treatment
alleviates the pollution by airborne organic solvents (Dyson et al., 1999).
At present, many researchers are seeking a cheaper alternative to [EMIM] [OAc],
which is nontoxic, robust to corrosion, and highly biodegradable but expensive to produce. To
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this end, they are testing the effectiveness of treating lignocellulosic materials with other ILs
(Maki-Arvela, Anugwom, Virtanen, Sjoholm & Mikkola, 2010).
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In this study, we reacted carboxylic acids of different chain lengths with aliphatic
amines under ambient conditions and obtained 14 new low-cost ILs. One of these ILs, n-
butylammonium acetate was used in the treatment of coir fiber. To increase the conversion of
cellulose to fermentable sugars, the fiber was first pulped to reduce its crystallinity.
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2. Material and methods
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2.1. Materials
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Methanoic acid (95%), acetic acid (99.7%), propanoic acid (99.5%), hexanoic acid
(99.5%), octanoic acid (98%), decanoic acid (98%), oleic acid (99%), n-butylamine (99.5%),
sec-butylamine (99%), sodium hydroxide, potassium hydroxide, and sulfuric acid (95.0–
98.0%) were purchased from Sigma Aldrich (USA). All reagents were analytical grade. Green
coir fiber (length 12–14 cm) was supplied by Projeto Coco Vivo (Arraial d'Ajuda – BA,
Brazil), and acetonitrile for high-performance liquid chromatography (HPLC) was purchased
from Sigma Aldrich.
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2.2. IL synthesis
ILs were synthesized by an acid–base neutralization reaction (Dyson et al., 1999). The
reaction was conducted by slow addition of carboxylic acid (methanoic acid 95%, acetic acid
99.7%, propanoic acid 99.5%, hexanoic acid 99.5%, octanoic acid 98%, decanoic acid 98%,
or oleic acid 99%) to aliphatic amine (n-butylamine 99.5% or sec-butylamine 99%) with
stirring. The stoichiometric ratio was 1:1. The addition was continued over 2 h, maintaining
the reaction temperature between 15 and 20 °C. After the addition, the obtained IL was stirred
for a further 60 min at 300 rpm and maintained in an amber bottle for 48 h.
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The prepared ILs were characterized by nuclear magnetic resonance (NMR) and infra-
red (IR) spectrometry at the Chemistry Institute, UNESP, in the city of Araraquara, SP,
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Brazil. The H and 13C NMR spectra were obtained in an Avance III 600 HD Bruker
spectrometer (Germany) operating at 600 MHz for protons and 150 MHz for carbon. The
solvent was CDCL3. The chemical shifts (δ, ppm) were reported relative to tetramethylsilane
(TMS). The IR spectra were obtained in Fourier Transform Infrared Spectroscopy Nicolet
with Attenuated Total Reflectance (FTIR–ATR) (model 6700, EUA) using 32 scans per
spectrum at a spectral resolution of 4 cm−1 in the wavenumber range 4000–450 cm−1.
Bidimensional spectra were acquired by homonuclear correlation spectroscopy (the
COSY technique), heteronuclear single quantum coherence (HSQC), and heteronuclear
multiple bond coherence (HMBC). These spectra revealed the correlations between
neighboring hydrogens and between neighboring hydrogens and carbons, thereby assisting the
assignment of hydrogen and carbon signals.
The synthesized ILs were n-butylammonium methanoate (1), sec-butylammonium
methanoate (2), n-butylammonium acetate (3), sec-butylammonium acetate (4), n-
butylammonium propanoate (5), sec-butylammonium propanoate (6), n-butylammonium
hexanoate (7), sec-butylammonium hexanoate (8), n-butylammonium octanoate (9), sec-
butylammonium octanoate (10), n-butylammonium decanoate (11), sec-butylammonium
decanoate (12), n-butylammonium oleate (13), and sec-butylammonium oleate (14) (Figure
1).
2.3. Treatment of coir fiber
The coir fibers were dried at 70 ± 3 °C for 72 h and ground in a Wiley-type cutting
mill (Tecnal model TE-6500; Brazil) using a 3-mm screen. The ground fibers were then
chemically pulped in a stainless steel reactor (Metalquim; Brazil) with a 5-l capacity. The
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pulping process was conducted in 8% (w/w) sodium hydroxide for 6 h. The pressure, rotation
speed, and temperature of pulping were maintained at 2.5 atm, 400 rpm, and 137 °C,
respectively. The pulped fiber was filtered, washed, and dried at 70 °C.
Following this, the pulped coir fiber was pretreated with n-butylammonium acetate (3)
for 2 h. The temperature and stirring rate of the IL pretreatment were maintained at 90 °C and
350 rpm, respectively. After the treatment, water was added to the mixture. The material was
then filtrated, washed to remove residual IL, and dried at 70 °C. The lignin and holocellulose
concentrations of the material were determined, and the delignification, surface changes, and
crystallinity changes of the coir fiber were confirmed by scanning electron microscopy
(SEM), X-ray diffraction (XRD), and FTIR–ATR analyses.
2.4. Acid hydrolysis
All acid hydrolysis reactions were conducted in duplicate. The data were analyzed by
Statistica 12.0 software (StatSoft Inc., 2014, Oklahoma, USA) using the central composite
rotatable design (CCRD) with two center points (Table 1). The input variables were the acetic
acid concentration (X1) and temperature (°C) (X2), and the output variable was the
fermentable sugar concentration (Y). The analysis was based on the Design of Experiments, a
well-known technique that simultaneously varies all parameters to maximize the obtained
information. This technique reduces the number of time-consuming numerical tests.
To validate the proposed model, we selected the parameters that most benefitted the
cellulose hydrolysis. Finally, the conditions that maximized the percentage of fermentable
sugars were determined by the desirability function D, defined as the geometric mean of all
individual desirabilities:
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D =m d1d2 …..dm ,
(1)
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where D denotes an individual desirability and m is the number of analyzed parameters.
To optimize the hydrolysis time, we varied the reaction time as 3, 6, 9, 12, and 24 h
and analyzed the final concentration of fermentable sugars by HPLC.
2.5. Characterization of coir fibers
The raw, pulped, and IL-treated pulped coir fibers were characterized by determining
their lignin (TAPPI test method T222 os-76, 1979), holocellulose (Wise & Murphy, 1946),
cellulose and hemicellulose (TAPPI T 203 cm-99, 1979) concentrations.
IR spectra were obtained by FTIR–ATR under the parameter settings described in
2.2.The fiber surfaces were observed by SEM (Obducat CamScan CS 3200 LV; Shimadzu,
Japan) under high vacuum (10–5 mbar). The images were acquired at an accelerating voltage
of 20 kV, a spot size of 3.00, and a working distance of 15 mm. The magnification was 500×.
XRD analysis was performed in an X-ray diffractometer (Shimadzu model 7000;
Japan). The operation voltage and current were maintained at 40 kV and 35 mA, respectively,
and the angular range was 3–135°. The diffraction spectra were collected using the θ–2θ
method. The samples were scanned from 3 to 40° 2
θ in steps of 0.020. The radiation
wavelength (sourced from Cu KαX-rays) was 1.5406 Å. The degree of crystallinity (Xc) was
calculated as the ratio of the area under the crystalline peaks to the area under the
noncrystalline region. That is,
F
c
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Xc =
×100,
(2)
F +F
a
c
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where Xc is the degree of crystallinity and Fc and Fa are the areas under the crystalline and
noncrystalline regions, respectively.
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2.6. Quantification of fermentable sugars
All hydrolysis products were characterized by HPLC using an LC-20AD
chromatograph (Shimadzu, Japan). The mobile phase was 0.005 mol l−1 sulfuric acid solution
flowing at 0.7 ml min−1. The column was a C18 CLC-ODS with a CLC ODS pre-column. The
detector was a Refractive Index detector.
3. Results and discussion
3.1. Preparation and characterization of ILs
From carboxylic acids with different chain lengths (methanoic acid, acetic acid,
propanoic acid, hexanoic acid, octanoic acid, decanoic acid, and oleic acid) and aliphatic
amines (n-butylamine and sec-butylamine), we synthesized 14 ILs. All ILs were characterized
by H1NMR, C13NMR, and FTIR–ATR (Table 2).
On analyzing the spectra of the synthesized ILs, we observed that the chemical
displacements of the amino groups of
n-butylamine and sec-butylamine were altered after the
formation of -butylammonium and sec-butylammonium ions. This shift was attributed to the
n
protonation of the amino group and the altered multiplicity of the amine hydrogen signal.
Integration of hydrogens into the amines and ILs was confirmed by the presence of two and
three hydrogen signals in the spectra, respectively (Table 2).
Changes in the FTIR–ATR data were also attributed to amino group protonation,
corroborating the NMR results. Carbonyl absorption was also evident in these data. In
particular, the carboxylic acids displayed an intense band in the region of 1700 cm−1. In ILs,
this band was shifted to 1600 cm−1, corresponding to the carbonyl of carboxylic salts (Pavia,
Lampman, Kriz & Vyvyan, 2014; Silverstein, Webster & Kiemle, 2005).
On comparing the signals of
n
-butylamine and
n
-butylammonium ions, we observed
-butylamine and 5.30,
that the chemical displacement of the amino group was 0.99 ppm in
n
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5.23, 8.64, 8.37, 7.96, 6.34, 7.59, 7.14, 6.33, 7.14, 7.03, 7.05, 5.40, and 5.80 ppm in ILs 1–14,
respectively (Xu, 2013; Xu, Yao, Wang & Li, 2012; Pavia et al., 2014; Silverstein et al.,
2005). The integrated signal of the amino group in the H1NMR spectrum also changed,
indicating the presence of three hydrogens in ILs.
The chemical displacement of the other signals was also increased in ILs, although it
was to a lesser extent than that in the amino group because of smaller shielding. Meanwhile,
the signal attributed to amino hydrogens was increased in the
n-butylammonium ions because
the exchange speed of hydrogens linked to the nitrogen atom was altered from that of
n
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butylamine; this was again consistent with the expected results (Table 2) (Pavia et al., 2014;
Silverstein et al., 2005).
The band around 1700 cm−1, corresponding to the C=O bond of the carboxylic acid
group, was also displaced by hydroxyl deprotonation and carboxylate ion formation in the IL
spectra.
3.2. Treatment of coir fiber
The fermentable sugar yields of hydrolyzed lignocelluloses can be improved by
various treatments. In this study, the lignin content of the coir fiber was reduced by two
treatments of the synthesized IL. IL treatment also modified the fiber crystallinity (Zhuo et al.,
2015; Gabhane et al., 2015; Bian et al., 2014; Morandim-Giannetti et al., 2013; Karthika,
Arun & Rekha, 2012).
The pulping process delignified the raw material by 64.42% and concentrated its
holocellulose by 13.50%. The holocellulose concentration was 73.50 ± 0.99% in the crude
fiber, and 83.43 ± 0.11% in the pulped fiber. Meanwhile, the lignin concentration was
determined as 30.1% ± 0.85 in the crude fiber and 10.71 ± 0.71% in the fiber treated with
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soda. Similar changes in fiber composition have been reported in other studies, corroborating
the obtained results (Gabhane et al., 2015; Bian et al., 2014; Morandim-Giannetti et al., 2013)
As revealed in SEM analysis (Figure 2A and 2B), the delignification increased the
cellulose exposure because the application of basic solutions at elevated temperatures and
pressures induces oxidative reactions that break down the lignin polymeric structure (Figure
3).
The micrographs in Figure 2A and 2B show the smooth surface and coated fibrils of
the untreated coir fibers, respectively. NaOH treatment removes the outer fiber material,
thereby roughening and pitting the fibers as the surface components are partially removed.
Along with the measured lignin and holocellulose concentrations, these micrographs indicate
that NaOH treatment removes surface lignin and components such as pectins, waxes, fatty
acids, and impurities.
The second treatment with n-bultilammonium acetate did not significantly modify the
lignin and holocellulose concentration (measured as 9.08 ± 0.88 and 91.48 ± 0.37,
respectively). Such minor concentration changes had no effect on the fiber surface after the
pulping process (Figure 2C) but significantly altered the fiber crystallinity, which favored the
subsequent hydrolysis because the cellulose was dissolved and regenerated after the water
addition (Zhuo et al., 2015; Bian et al., 2014 ).
The SEM image (Figure 2C) confirms that the administered IL treatment had little
effect on the fiber structure, yet it demonstrably improved the fermentable sugar yields from
the lignocellulosic material. This confirms the importance of IL treatment prior to hydrolysis.
These results are confirmed in the FTIR–ATR spectra, in which the absorption of the
O–H stretching vibration shifts from 3400 cm−1 in the original cellulose to 3300 cm−1 in the
regenerated cellulose after IL treatment. This shift reflects the increased content of free
hydroxyl groups in the regenerated cellulose due to the crystallinity changes. The absorption
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band, which shifts from 1427 cm−1 in crude cellulose to 1419 cm−1 in the regenerated IL-
treated cellulose, further consolidates the crystallinity change (Figure 4).
The XRD patterns (Figure 5) of the crude fiber display the typical diffraction peaks of
crystalline cellulose (θ = 15.00° and 22°, characterizing the 101 and 002 plane positions of
cellulose, respectively). These peaks were more intense and well-defined after soda and IL
treatment, reflecting the better packaging of cellulose microfibrils, which increases the
crystallinity in the treated samples (Li et al., 2015; Xu, et al., 2015).
Quantitatively, the crystallinities of crude fiber, pulped fiber, and pulped fiber treated
with
n-butylammonium acetate were 51.153%, 58.450%, and 59.511%, respectively,
consistent with previously reported results (Zhuo et al., 2015; Li et al., 2015; Bian et al.,
2014). IL treatment suggested that part of the resistant amorphous hemicellulose was
solubilized in IL, increasing the final cellulose concentration (Figure 6). This increase
facilitated the reducing sugar production after the acid hydrolysis by attenuating the
subproduct production.
3.3. Optimization of acid hydrolysis conditions of treated coir fiber
When the response of interest is affected by several variables, the number of
experiments in the process optimization is popularly reduced by statistical planning. In this
study, we used a statistical method to analyze the percentage of fermentable sugars obtained
after acid hydrolysis of the pulped coir fiber treated with n-butylammonium acetate.
Hydrolyses were duplicated under the conditions shown in Table 1. All samples were
analyzed by HPLC, and their glucose contents were calculated (Table 3). The statistical
model, implemented in Statistica 12.0 software, included linear and quadratic terms. As input
variables, we selected the variables that were most affected during the attainment of the
material (Table 4).
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The glucose concentration (Y) was not significantly altered under any of the
experimental conditions. The hydrolysis reaction was most sensitive to the temperature (X2).
This finding can be explained by the increase in free ion availability at higher temperatures,
which promotes the hydrolysis reaction. Moreover, the temperature must be sufficiently high
to activate the processing reaction.
These results were confirmed in further studies. Thus, through statistical analysis and
necessary restriction, we clarified that the conversion of cellulose into glucose was modified
to a greater extent by the temperature than by the acid concentration.
The input variables (X1 and X2) and output variables (Y) are related by Eq. 3. From
statistical analysis and necessary restrictions, the optimal acetic acid concentration and
temperature were obtained as 32.2% and 122.4 °C, respectively. Under these conditions, the
conversion of cellulose to fermentable sugars was demonstrably improved (Figure 7).
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Y = 7.309 + 0.568X1 + 0.357X2 − 0.002X1X2 − 0.005X12 + 0.003X22
R2 = 0.648
(3)
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A long reaction time, perhaps extended for many hours, encourages byproduct
formation and may reduce the concentration of fermentable sugars. After 3 h of reaction the
yield decreased, indicating that the reaction was disadvantaged (Figure 8).
After optimizing the hydrolysis conditions, the efficiency of the synthesized IL
treatment was experimentally evaluated. The conversion rate to fermentable sugars was
8.53% for crude fiber, 47.58% for pulped fiber, and 89.75% for pulped fiber treated with IL.
In comparison, Parveen et al. (2016) and Zhuo et al. (2016) obtained conversion rates of 85%
and 85.1%, respectively, after treatment with the IL solvent 1-butyl-3-methylimidazolium
chloride [BMIM]Cl. Xiao, Yin, Xia & Ma (2012) reported conversion rates of 90.72% and
88.92% after treatment with 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) and 1-
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butyl-3-methylimidazolium formate ([BMIM][HCOO]), respectively. These comparisons
confirm the efficiency of conversion by coir fiber treated with our low-cost IL.
4. Conclusion
In this study, we synthesized and characterized 14 low-cost ILs based on the
butylammonium cation. ILs were easily prepared under ambient conditions by reacting
carboxylic acids of different chain lengths with aliphatic amines. All the synthesized ILs are
RTILs and are applicable as alternative reagents in different chemical and biotechnological
processes.
Treatment of the coir fiber with n-butylammonium acetate favored the subsequent
hydrolysis process, increasing the productivity by more than 800%. Because IL is low cost
and boosts the efficiency of the hydrolysis, its larger scale synthesis should be investigated in
future study. The remaining synthesized ILs should also be tested.
5. Acknowledgements
We are grateful to Fundação Educacional Inaciana Padre Sabóia de Medeiros (FEI),
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and Fundação de
Amparo à Pesquisa do Estado de São Paulo (FAPESP) for supporting this research. We thank Dr.
Nivaldo Boralle for the NMR measurements.
6. References
Bahrani, S., Raeissi, S., Sarshar, M. (2015). Experimental investigation of ionic liquid
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440
441
Figure Caption
Figure 1: Ionic liquids obtained by acid base neutralization.
Figure 2: SEM micrographs obtained for crude fiber (A), pulping fiber (B) and IL-treated
fiber (C)
Figure 3: Oxidative breaking of the structure of lignin during pulping in a basic medium
Figure 4: Infrared spectra of crude fiber (A), pulping fiber (B) and IL-treated fiber (C)
Figure 5: XRD patterns of crude fiber (A), pulping fiber (B) and IL-treated fiber (C)
Figure 6: Lignin, cellulose and hemicellulose percentage of crude fiber (A), pulping fiber (B)
and IL-treated fiber (C)
442
443
444
445
446
447
Figure 7: Optimization of the conditions for obtaining fermentable sugar by hydrolysis
process
448
449
Figure 8: Illustrating the influence of time on the hydrolysis of coir fiber
Page 20 of 32

21
449
Table 1: Experimental CCRD conditions during the cellulose hydrolysis.
coded variables corresponding variables
% acetic acid (X1)
Temperature (X2)
% acetic acid (X1)
Temperature (X2)
0
-
5.70
15.00
15.00
37.50
80.0
50.00
110.00
37.60
-1
-1
0
-1
+1
-
0
0
0
0
0
37.50
37.50
37.50
60.00
60.00
69.30
80.00
80.00
122.40
50.00
110.0
80.00
+
+1
+1
+
-1
+1
0
450
451
1
452
453
Table 2: FT-IR vibrational frequencies (ν), HNMR and C13NMR chemical shifts (δ) for
n-
butylamine, sec-butylamine and ILs
IR (ν)/cm-1
1HNMR (δ)/ppm
13CNMR (δ)/ppm
ILs
n-butylamine
3500-3300 (N–H stretching vibration),
1608 (N-H in-plane-bend), 1093 (C-N
stretching vibration)
2.62 (t, 2H), 1.34 (m, 2H), 1.28 (m, 2H),
0.84 (t, 3H), 0.99 (s, 2H, NH2)
42.15, 36.04, 20.30, 13.90
Sec-butylamine
3500-3300 (N–H stretching vibration),
1600 (N-H in-plane-bend), 1162 (C-N
stretching vibration)
-0.65 (d, 3H), 2.39 (m, 1H), 0.94 (dm,
2H), 0.50 (t, 3H) 0.84 (s, 2H, NH2)
22.90, 47.59, 32.23, 10.02
3100-2600 (+N–H stretching vibration),
1623 (C=O stretching vibration), 1572
(+N–H bending vibration), 1467 (C–H
bending vibration)
8.48 (s, 1H), 2.85 (t, 2H), 1.62 (m, 2H),
1.35 (m, 2H), 0.93 (t, 3H), 5.30 (s, 3H,
168.87, 39.28, 29.47, 19.31,
14.12
1
2
3
4
5
+
NH3 )
3100-2500 (+N–H stretching vibration),
1620 (C=O stretching vibration), 1577
(+N–H bending vibration), 1462 (C–H
bending vibration)
8.52 (s, 1H), 1.27 (d, 3H), 3.11 (m, 1H),
1.63 (m, 2H), 0.97 (t, 3H), 5,23 (s, 3H,
169.68, 18.57, 48.69, 28.35,
10.03
+
NH3 )
3100-2450 (+N–H stretching vibration),
1600 (C=O stretching vibration), 1558
(+N–H bending vibration), 1467 (C–H
bending vibration)
1.90 (s, 3H), 2.77 (t, 2H), 1.58 (m, 2H),
1.34 (m, 2H), 0.88 (t, 3H), 8.64 (s, 3H,
178.07, 30.04, 38.58, 23.73,
19.29, 13.26
+
NH3 )
3100-2450 (+N–H stretching vibration), ,
1650 (C=O stretching vibration), 1558
(+N–H bending vibration), 1400 (C–H
bending vibration)
1.89 (s, 3H), 1.23 (d, 3H)), 3.01 (m,
1H), 1.46 e 1.69 (dm, 2H), 0.91 (t, 3H),
8.37 (s, 3H)
178.06, 28.17, 18.05, 48.03,
24.03, 9.47
3120-2500 (+N–H stretching vibration),
1650 (C=O stretching vibration), 1550
(+N–H bending vibration), 1401 (C–H
bending vibration)
.03 (m, 2H), 0.93 (t, 3H), 2.69 (t, 2H),
1.49 (m, 2H), 1.25(m, 2H), 0.78 (t, 3H),
181.80, 30.97, 13.25, 39.51,
30.26, 19.57, 10.74
+
7.96 (s, 3H, NH3 )
3110-2450 (+N–H stretching vibration),
1.72 (m, 2H), 1.10 (t, 3H), 1.26 (d, 3H),
181.74, 31.07, 10.88, 19.23,
Page 21 of 32

22
6
7
1655 (C=O stretching vibration), 1558
(+N–H bending vibration) 1400 (C–H
bending vibration)
3.05 (m 1H), 1.53 e 1.55 (dm, 2H), 0.97
48.85, 29.10, 10.45
+
(t, 3H), 6.34 (s, 3H, NH3 )
3150-2500 (+N–H stretching vibration),
1629 (C=O stretching vibration), 1558
(+N–H bending vibration), 1400 (C–H
bending vibration)
2.01 (t, 2H), 1.38 (m, 2H), 1.12 (m, 2H),
1.20 (m, 2H), 0.77 (t, 3H), 2.59 (t, 2H),
1.44 (m, 2H), 1.12 (m, 2H), 0.75 (t, 3H),
181.53, 38.51, 30.49, 20.10,
26.52. 14.19, 39.49. 32.19,
22.65, 13.80
+
7.59 (s, 3H, NH3 )
3100-2500 (+N–H stretching vibration),
1629 (C=O stretching vibration), 1558
(+N–H bending vibration), 1400 (C–H
bending vibration)
2.14 (t, 2H), 1.55 (m, 2H), 1.30 (m, 2H),
1.27 (m, 2H), 0.88 (t, 3H), 1.22 (d, 3H),
2.99 (m, 1H), 1.54 e 1.57 (dm, 2H), 0.94
180.66, 37.87, 26.07, 22.56,
31.90, 14.04 , 19.07, 48.51,
28.93, 10.15
8
+
(t, 3H), 7.14 (s, 3H, NH3 )
3110-2500 (+N–H stretching vibration),
1600 (C=O stretching vibration), 1556
(+N–H bending vibration), 1400 (C–H
bending vibration)
2.17 (t, 2H), 2.55 (m, 2H), 1.28 (m, 8H),
0.87 (t, 3H), 2.80 (t, 2H), 1.60 (m, 2H),
1.36 (m, 2H), 0.92 (t, 3H), 6.33 (s, 3H,
181.81, 37.49, 26.26, 30.51,
29.69, 29.32, 22.79, 14.22,
39.50, 32.00, 19.99, 13.74
9
+
NH3 )
3110-2500 (+N–H stretching vibration),
1629 (C=O stretching vibration), 1559
(+N–H bending vibration), 1400 (C–H
bending vibration)
2.10 (t, 2H), 1.52 (m, 2H), 1.26 (m, 6H),
1.22 (m, 2H), 0.85 (t, 3H), 1.21 (2, 3H),
2.98 (m, 1H), 1.46 e 1.67 (dm, 2H), 0.93
181.16, 38.80, 26.71, 31.95,
29.85, 29.35, 22.78, 14.21,
18.78, 48.60, 28.86, 10.22
10
11
12
+
(t, 3H), 7.14 (s, 3H, NH3 )
3100-2500 (+N–H stretching vibration),
1629 (C=O stretching vibration), 1559
(+N–H bending vibration), 1400 (C–H
bending vibration)
2.14 (t, 2H), 1.53 (m, 2H), 1.25 (m,
12H), 0.86 (t, 3H), 2.78 (t, 2H), 1.60 (m,
2H), 1.36 (m, 2H), 0.92 (m, 2H), 7.03 (s,
181.36, 37.82, 26.42, 32.14,
29.93, 29.73, 29.49, 26.42,
22.81, 14.24, 39.43, 30.44,
20.00, 13.68
180.82, 37.84, 26.43, 32.04,
29.82, 29.72, 29.69, 29.48,
22.82, 14.25, 18.53, 48.68,
28.45, 10.19
180.57, 37.96, 26.50, 32.00,
29.91, 29.83, 29.47, 130.02,
129.92, 27.37, 25.65, 22.83,
22.50, 14.26, 19.27, 48.57,
29.45, 10.29
+
3H, NH3 )
3110-2500 (+N–H stretching vibration),
1629 (C=O stretching vibration), 1559
(+N–H bending vibration), 1400 (C–H
bending vibration)
2.13 (t, 2H), 1.54 (m, 2H), 1.24 (m,
12H), 0.87 (t, 3H), 1.23 (d, 3H), 3.02
(m, 1H), 1.48 e 1.71 (m, 2H), 0.94 (t,
+
3H), 7.05 (s, 3H, NH3 )
3050-2500 (+N–H stretching vibration),
1600 (C=O stretching vibration), 1558
(+N–H bending vibration), 1400 (C–H
bending vibration)
2.18 (t, 2H), 1.56 (m, 2H), 1.29 (m,
14H), 1.35 (m, 4H), 2.00 (m, 4H),
5.31(m, 1H, J = 6 Hz), 5.32 (m, 1H, J =
6 Hz), 1.26 (m, 2H), 0.87 (m, 2H), 2.78
(t, 2H)), 1.56 (m, 2H), 1.29 (m, 2H),
13
14
+
0.92 (t, 3H), 5.40 (s, 3H, NH3 )
3030-2500 (+N–H stretching vibration),
1629 (C=O stretching vibration), 1565
(+N–H bending vibration), 1400 (C–H
bending vibration)
2.15 (t, 2H), 1.55 (m, 2H), 1.28 (m,
16H), 2.00 (m, 4H), 5.33 (m, 1H, J = 6
Hz), 5.34 (m, 1H, J = 6 Hz), 1.22 (m,
4H), 0.87 (t, 3H), 1.20(d, 3H), 2.98 (m,
1H), 1.48 e 1.65 (dm, 2H), 0.94 (10.29),
180.57, 37.96, 26.50, 32.00,
29.91, 29.83, 29.47, 130.02,
129.92, 27.37, 25.65, 22.83,
22.50, 14.26, 19.27, 48.57,
29.45, 10.29
+
5.80 (s, 3H, NH3 )
454
* where: (d) doublet, (dm) double multiplet, (m) multiplet, (s) singlet and (t) triplet
455
456
Table 3: Concentration of fermentable sugars obtained from each sample
acetici acid (%)
(X1)
Temperature (ºC)
(X2)
Glucose (%)
(Y)
2.50
5.70
80.00
4.26
15.00
50.00
6.73
15.00
110.00
37.60
8.53
37.50
6.31
37.50
80.00
8.53
37.50
80.00
22.30
6.49
37.50
122.40
50.00
60.00
3.93
60.00
110.00
80.00
6.34
69.30
Page 22 of 32

23
457
458
459
460
Table 4: Effect of acetic acid concentration (X1) and temperature (X2) on glucose
concentration (Y)
Effect Estimates; Var.:Y; R-sqr=.64749; Adj:.20684 MS Residual=24.11397
Effect
Std.Err.
t(4)
p
-95.%
+95.%
Coeff. Std.Err.
-95.%
+95.%
(Cnf.Limt) (Cnf.Limt)
(Coeff.) (Cnf.Limt)
(Cnf.Limt)
Factor
Mean/Interc. 7.427
3.472
3.473
4.597
3.473
4.597
4.911
2.139
0.349
-1.152
1.396
1.242
-0.513
0.099
0.744
0.313
0.235
0.282
0.635
-2.213
-8.430
-18.060
-4.796
-7.053
-16.151
17.068
10.857
7.468
7.427
0.607
-2.648
2.424
2.855
-1.259
3.472
1.737
2.299
1.737
2.299
2.455
-2.213
-4.215
-9.030
-2.398
-3.526
-8.076
17.068
5.429
3.734
7.246
9.237
5.558
(1)X1(L)
X1(Q)
1.214
-5.296
4.848
5.711
-2.517
(2)X2(L)
X2(Q)
14.491
18.474
11.117
1L by 2L
461
462
Highlights
463
464
Synthesis of new low cost Ionic Liquid and application in coir fiber treatment for bioethanol
production
465
466
467
Determination of the best conditions for acid hydrolysis of coir fiber
Efficiency of the acid hydrolysis of coir fiber after treatment with Ionic Liquid
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