Structural evaluation of sugar cane bagasse steam pretreated in the presence of CO2 and SO2

De, Corrales, Mendes, Perrone Clarissa, Sant’Anna Celso, Abud Yuri, Bon, Ferreira-Leitão, Ferreira-Leitão Viridiana

Description

Previous studies on the use of SO 2 and CO 2 as impregnating agent for sugar cane bagasse steam treatment showed comparative and promising results concerning the cellulose enzymatic hydrolysis and the low formation of the inhibitors furfural and hydroxymethylfurfural for the use of CO 2 at 205°C/15 min or SO 2 at 190°C/5 min. In the present study sugar cane bagasse materials pretreated as aforementioned were analyzed by scanning and transmission electron microscopy (SEM and TEM), X-Ray Diffraction (XRD) and Infrared (FTIR spectroscopy) aiming a better understanding of the structural and chemical changes undergone by the pretreated materials. Results SEM and TEM data showed that the structural modifications undergone by the pretreatment with CO 2 were less pronounced in comparison to that using SO 2, which can be directly related to the combined severity of each pretreatment. According to XRD data, untreated bagasse showed, as expected, a lower crystallinity index (CI = 48.0%) when compared to pretreated samples with SO 2 (CI = 65.5%) or CO 2 (CI = 56.4%), due to the hemicellulose removal of 68.3% and 40.5%, respectively. FTIR spectroscopy supported SEM, TEM and XRD results, revealing a more extensive action of SO 2 . Conclusions The SEM, TEM, XRD and FTIR spectroscopy techniques used in this work contributed to structural and chemical analysis of the untreated and pretreated bagasse. The images from SEM and TEM can be related to the severity of SO 2 pretreatment, which is almost twice higher. The crystallinity index values obtained from XRD showed that pretreated materials have higher values when compared with untreated material, due to the partial removal of hemicellulose after pretreatment. FTIR spectroscopy supported SEM, TEM and XRD results. CO 2 can actually be used as impregnating agent for steam pretreatment, although the present study confirmed a more extensive action of SO 2 .

Informations

• Publié par: biomed
• Publié le: 01 janvier 2012
• Nombre de lectures: 14
• Langue: EnglishEnglish
• Poids de l'ouvrage: 1 Mo

Extrait

Corrales et al. Biotechnology for Biofuels 2012, 5:36
http://www.biotechnologyforbiofuels.com/content/5/1/36
RESEARCH Open Access
Structural evaluation of sugar cane bagasse
steam pretreated in the presence of CO and SO2 2
1 1 1Roberta Cristina Novaes Reis Corrales , Fabiana Magalhães Teixeira Mendes , Clarissa Cruz Perrone ,
2,3 2,3 2 4 1,4*Celso Sant’Anna , Wanderley de Souza , Yuri Abud , Elba Pinto da Silva Bon and Viridiana Ferreira-Leitão
Abstract
Background: Previous studies on the use of SO and CO as impregnating agent for sugar cane bagasse steam2 2
treatment showed comparative and promising results concerning the cellulose enzymatic hydrolysis and the low
formation of the inhibitors furfural and hydroxymethylfurfural for the use of CO at 205°C/15 min or SO at2 2
190°C/5 min. In the present study sugar cane bagasse materials pretreated as aforementioned were analyzed by
scanning and transmission electron microscopy (SEM and TEM), X-Ray Diffraction (XRD) and Infrared (FTIR
spectroscopy) aiming a better understanding of the structural and chemical changes undergone by the pretreated
materials.
Results: SEM and TEM data showed that the structural modifications undergone by the pretreatment with CO were2
less pronounced in comparison to that using SO which can be directly related to the combined severity of each2,
pretreatment. According to XRD data, untreated bagasse showed, as expected, a lower crystallinity index
(CI = 48.0%) when compared to pretreated samples with SO (CI = 65.5%) or CO (CI = 56.4%), due to the2 2
hemicellulose removal of 68.3% and 40.5%, respectively. FTIR spectroscopy supported SEM, TEM and XRD results,
revealing a more extensive action of SO .2
Conclusions: The SEM, TEM, XRD and FTIR spectroscopy techniques used in this work contributed to structural and
chemical analysis of the untreated and pretreated bagasse. The images from SEM and TEM can be related to the
severity of SO pretreatment, which is almost twice higher. The crystallinity index values obtained from XRD showed2
that pretreated materials have higher values when compared with untreated material, due to the partial removal of
hemicellulose after pretreatment. FTIR spectroscopy supported SEM, TEM and XRD results. CO can actually be used as2
impregnating agent for steam pretreatment, although the present study confirmed a more extensive action of SO .2
Keywords: Sugar cane bagasse, CO and SO steam pretreatment, SEM and TEM microscopy, XRD and FTIR2 2
spectroscopy
Background first generation (1G) ethanol. The residual lignocellulosic
There is a growing urgency to develop novel bio-based biomass from the 1G ethanol industry (sugar cane ba-
products and other innovative technologies that can gasse and leaves) is, presently, for a collection of reasons,
overcome the widespread dependence on fossil fuels [1]. the most promising resource for the production of ligno-
Unlike gasoline, ethanol is a renewable energy source cellulosic (2G) ethanol [2]. However, although the sugar-
produced through fermentation of sugar. In Brazil, etha- ethanol industry generates bagasse in large quantities
nol is produced largely from sugar cane juice, known as during the process of extraction of the sugar cane juice
it is mostly used for co-generation, accounting for ap-
proximately 3% of the electricity available in Brazil [3].
* Correspondence: [e-mail]
1 Lignocellulosic biomass is mainly composed of cellulose,
National Institute of Techonology, Ministry of Science and Techonology,
hemicellulose and lignin. The predominant component ofAv. Venezuela, 82, sala 302, CEP 20081-312 Rio de Janeiro - RJ, Brazil
4
Department of Biochemistry, Institute of Chemistry, Federal University of Rio lignocellulosic biomass is cellulose, a linear β (1,4)-linked
de Janeiro, Av. Athos da Silveira Ramos, 149, bloco A, Ilha do Fundão, CEP:
chain of glucose molecules. It is non-toxic, renewable,
21941-909 Rio de Janeiro - RJ, Brazil
biodegradable, modifiable and has great potential as anFull list of author information is available at the end of the article
© 2012 Corrales et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.Corrales et al. Biotechnology for Biofuels 2012, 5:36 Page 2 of 8
http://www.biotechnologyforbiofuels.com/content/5/1/36
excellent industrial material [4,5]. The elementary fibrils Results and discussion
are composed of crystalline and amorphous regions. Scanning electron microscopy (SEM) and transmission
Hemicelluloses are made up of C5 and C6 sugar, such as electron microcopy (TEM)
xylose, arabinose, galactose, glucose and mannose. Lignin The use of scanning electron microscopy as an analytical
accounts for about one fourth of the lignocellulosic bio- technique proved to be of great importance and versatility
mass andis thethird mostabundantbiopolymeronly after for studying the biomass structure. Figure 1 shows the
celluloseand hemicellulose. morphological characteristics of the steam pretreated ba-
According to Fengel and Wegener [6], four elementary gasse in the presence of CO or SO as well as of the un-2 2
fibrils of cellulose are held together by a monolayer of treated material, obtained by scanning electron microscopy
hemicellulose, which generate 25 nm wide thread-like (SEM).
structures that are enclosed in a matrix of hemicellulose Untreated bagasse sample (Figure 1A, B, C) presents a
and lignin (associated with each other through physical rigid and compact morphology, while the ones submit-
interactions and covalent bonds). ted to pretreatment with SO (Figure 1D, E, F) or CO2 2
The main steps for ethanol production from lignocel- (Figure 1G, H, I) exhibited a more disorganized morph-
lulosic biomass are pretreatment, hydrolysis, fermenta- ology, with greater exposure of the fibers.
tion and distillation/purification. The pretreatment After pretreatment, the most exposed cell wall structure
should enhance the fiber accessibility and consequently allows for a greater accessibility to hydrolytic enzymes,
facilitate the subsequent steps of enzymatic hydrolysis which facilitates the hydrolysisoflignocellulosic biomass.
and fermentation [7]. Transmission electron microscopy (TEM) has been
The raw material pretreatment step could represent up used as a suitable method to determine the effect of pre-
to 20% of the total costs of cellulosic ethanol production treatment within the plant cell wall [15]. TEM images of
[8]. According to Galbe and Zacchi [9], an effective pre- untreated sugar cane bagasse clearly showed that the
treatment should (a) improve cellulose digestibility; (b) pro- primary cell wall (PCW), secondary cell wall (SCW) and
duce low concentrations of degradation products derived middle lamella (ML) were well preserved (Figure 2A, B).
from sugars and lignin; and (c) have a low energy demand. These structures were bonded strongly together giving
Previous studies on steam pretreatment of bagasse rise to a typical highly compact architecture of cell walls.
employed CO as impregnating agent to replace the As it is a thicker and more rigid structure in the bagasse,2
traditionally used SO [10]. The use of CO was previ- the SCW, where cellulose microfibrils are arranged in2 2
ously investigated in order to explore some advantages parallel position, is responsible for cell wall integrity
of this gas over SO , such as high availability in the first- (Figure 2B). The pretreated CO samples show, in the2 2
generation ethanol plants, low toxicity, low corrosivity cell wall, large pores with different size and shape
and low occupational risk [10,11]. Although the use of (Figure 2C, D).Remarkably, most of the pores were formed
CO provided equivalent results in comparison to those in the outer region of the cell wall. When SO was used as2 2
obtained when SO was used as impregnating agent, impregnating agent, the secondary cell wall, especially the2
higher temperatures or longer times were necessary. outer region, was also severely disrupted leading to the
Comparative results concerning glucose release and inhi- appearance of large irregular shaped pores (Figure 2E, F) as
bitors formation (furfural and hydroxymethylfurfural – a result of partial solubilization of ultrastructural cell wall
HMF) from steam pretreatedbagasse wereobtained under components. Similar results were recently reported by
the conditions: 205°C/15 min using CO or 190°C/5 min Chundawat and co-workers [15] in corn stover after am-2
using SO . As previously reported by authors [10], the use monia fiber expansion (AFEX) treatment.2
of SO resulted in 79.7% of glucose after enzymatic hy- The AFEX pretreatment strategy revealed that cellulose2
drolysis and provided the formation of 0.80 g/100g of fur- hydrolysis increased roughly five-fold when compared to
fural and 0.18 g/100g of HMF (dry bagasse). When CO untreated samples. In addition, when both CO and SO2 2 2
was employed, the yield of glucose reached 86.6% and the were employed, coalescent particles with round or elon-
values for furfural (0.9 g/100g) and HMF (0.2 g/100g) were gated shapes were found in the cell wall (Figure 2D, F).
very similar tothose reported for SO They seem to be formed by the process of coalescence of2.
FTIR spectro